Ôn tập: Tính chất cơ bản của phân số
<h3 id="a-tiacutenh-chat-co-ban-cua-phacircn-so">a) Tính chất cơ bản của phân số</h3> <p>• Nếu nhân cả tử số và mẫu số của một phán số với cùng một số tự nhiên khác 0 thì được một phân số bằng phân số đã cho.</p> <p>• Nếu chia hết cả tử số và mẫu số của một phân số cho cùng một số tự nhiên khác 0 thì được một phân số bằng phân số đã cho.</p> <p>Ví dụ 1:&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="0" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c36"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>5</mn><mn>6</mn></mfrac></math></mjx-assistive-mml></mjx-container>= <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="1" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c35"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cD7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-mrow></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c36"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cD7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-mrow></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>5</mn><mo>&nbsp;</mo><mo>×</mo><mo>&nbsp;</mo><mn>3</mn></mrow><mrow><mn>6</mn><mo>&nbsp;</mo><mo>×</mo><mo>&nbsp;</mo><mn>3</mn></mrow></mfrac></math></mjx-assistive-mml></mjx-container> = <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="2" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c38"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>15</mn><mn>18</mn></mfrac></math></mjx-assistive-mml></mjx-container></p> <p>Ví dụ 2:&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="3" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c38"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>15</mn><mn>18</mn></mfrac></math></mjx-assistive-mml></mjx-container>= <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="4" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c35"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cF7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-mrow></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c38"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cF7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-mrow></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>15</mn><mo>&nbsp;</mo><mo>÷</mo><mo>&nbsp;</mo><mn>3</mn></mrow><mrow><mn>18</mn><mo>&nbsp;</mo><mo>÷</mo><mo>&nbsp;</mo><mn>3</mn></mrow></mfrac></math></mjx-assistive-mml></mjx-container> =&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="5" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c36"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>5</mn><mn>6</mn></mfrac></math></mjx-assistive-mml></mjx-container></p> <h3 id="b-ung-dung-tiacutenh-chat-co-ban-cua-phacircn-so">b) Ứng dụng tính chất cơ bản của phân số</h3> <p>• Rút gọn phân số.</p> <p>Ví dụ: <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="6" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c39"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c32"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>90</mn><mn>120</mn></mfrac></math></mjx-assistive-mml></mjx-container> =&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="7" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c39"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cF7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-mrow></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c32"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cF7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-mrow></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>90</mn><mo>&nbsp;</mo><mo>÷</mo><mo>&nbsp;</mo><mn>10</mn></mrow><mrow><mn>120</mn><mo>&nbsp;</mo><mo>÷</mo><mo>&nbsp;</mo><mn>10</mn></mrow></mfrac></math></mjx-assistive-mml></mjx-container> = <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="8" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c39"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>9</mn><mn>12</mn></mfrac></math></mjx-assistive-mml></mjx-container> = <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="9" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c39"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cF7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-mrow></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c32"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cF7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-mrow></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>9</mn><mo>&nbsp;</mo><mo>÷</mo><mo>&nbsp;</mo><mn>3</mn></mrow><mrow><mn>12</mn><mo>&nbsp;</mo><mo>÷</mo><mo>&nbsp;</mo><mn>3</mn></mrow></mfrac></math></mjx-assistive-mml></mjx-container> = <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="10" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c34"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>3</mn><mn>4</mn></mfrac></math></mjx-assistive-mml></mjx-container></p> <p>hoặc:&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="11" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c39"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c32"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>90</mn><mn>120</mn></mfrac></math></mjx-assistive-mml></mjx-container> =&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="12" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c39"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cF7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c33"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-mrow></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c32"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cF7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c33"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-mrow></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>90</mn><mo>&nbsp;</mo><mo>÷</mo><mo>&nbsp;</mo><mn>30</mn></mrow><mrow><mn>120</mn><mo>&nbsp;</mo><mo>÷</mo><mo>&nbsp;</mo><mn>30</mn></mrow></mfrac></math></mjx-assistive-mml></mjx-container> =&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="13" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c34"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>3</mn><mn>4</mn></mfrac></math></mjx-assistive-mml></mjx-container>;...</p> <p>• Quy đồng mẫu số các phân số.</p> <p>Ví dụ 1: Quy đồng mẫu số của <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="14" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>2</mn><mn>5</mn></mfrac></math></mjx-assistive-mml></mjx-container>và <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="15" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c34"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c37"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>4</mn><mn>7</mn></mfrac></math></mjx-assistive-mml></mjx-container>.</p> <p>Lấy tích 5 <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="16" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mo class="mjx-n"><mjx-c class="mjx-cD7"></mjx-c></mjx-mo></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>×</mo></math></mjx-assistive-mml></mjx-container> 7 = 35 là mẫu số chung (MSC). Ta có:</p> <p><mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="17" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>2</mn><mn>5</mn></mfrac></math></mjx-assistive-mml></mjx-container> =&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="18" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c32"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cD7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c37"></mjx-c></mjx-mn></mjx-mrow></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c35"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cD7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c37"></mjx-c></mjx-mn></mjx-mrow></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>2</mn><mo>&nbsp;</mo><mo>×</mo><mo>&nbsp;</mo><mn>7</mn></mrow><mrow><mn>5</mn><mo>&nbsp;</mo><mo>×</mo><mo>&nbsp;</mo><mn>7</mn></mrow></mfrac></math></mjx-assistive-mml></mjx-container>=<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="19" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c34"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>14</mn><mn>35</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp;&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="20" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c34"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c37"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>4</mn><mn>7</mn></mfrac></math></mjx-assistive-mml></mjx-container> =&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="21" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c34"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cD7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-mrow></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c37"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cD7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-mrow></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>4</mn><mo>&nbsp;</mo><mo>×</mo><mo>&nbsp;</mo><mn>5</mn></mrow><mrow><mn>7</mn><mo>&nbsp;</mo><mo>×</mo><mo>&nbsp;</mo><mn>5</mn></mrow></mfrac></math></mjx-assistive-mml></mjx-container> =&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="22" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c32"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>20</mn><mn>35</mn></mfrac></math></mjx-assistive-mml></mjx-container>.</p> <p>Ví dụ 2: Quy đồng mẫu số của <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="23" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>3</mn><mn>5</mn></mfrac></math></mjx-assistive-mml></mjx-container>và <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="24" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c39"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>9</mn><mn>10</mn></mfrac></math></mjx-assistive-mml></mjx-container>.</p> <p>Nhận xét: 10 : 5 = 2, chọn 10 là mẫu số chung (MSC). Ta có:</p> <p><mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="25" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>3</mn><mn>5</mn></mfrac></math></mjx-assistive-mml></mjx-container> = <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="26" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c33"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cD7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-mrow></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mrow size="s"><mjx-mn class="mjx-n"><mjx-c class="mjx-c35"></mjx-c></mjx-mn><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cD7"></mjx-c></mjx-mo><mjx-mo class="mjx-n"><mjx-c class="mjx-cA0"></mjx-c></mjx-mo><mjx-mn class="mjx-n"><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-mrow></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>3</mn><mo>&nbsp;</mo><mo>×</mo><mo>&nbsp;</mo><mn>2</mn></mrow><mrow><mn>5</mn><mo>&nbsp;</mo><mo>×</mo><mo>&nbsp;</mo><mn>2</mn></mrow></mfrac></math></mjx-assistive-mml></mjx-container> = <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="27" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c36"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>6</mn><mn>10</mn></mfrac></math></mjx-assistive-mml></mjx-container>; giữ nguyên <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="28" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c39"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>9</mn><mn>10</mn></mfrac></math></mjx-assistive-mml></mjx-container>.</p> <h3 id="bagravei-tap">Bài tập</h3> <h4>1.Rút gọn các phân số:</h4> <p><mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="29" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c32"></mjx-c><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>15</mn><mn>25</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp; <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="30" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c38"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c32"></mjx-c><mjx-c class="mjx-c37"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>18</mn><mn>27</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp; <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="31" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c><mjx-c class="mjx-c34"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c36"></mjx-c><mjx-c class="mjx-c34"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>34</mn><mn>64</mn></mfrac></math></mjx-assistive-mml></mjx-container>.</p> <h4>2.Quy đồng mẫu số các phân số:</h4> <p>a) <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="32" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>2</mn><mn>3</mn></mfrac></math></mjx-assistive-mml></mjx-container> và <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="33" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c38"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>5</mn><mn>8</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp; b) <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="34" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c34"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>1</mn><mn>4</mn></mfrac></math></mjx-assistive-mml></mjx-container> và <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="35" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c37"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>7</mn><mn>12</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp;c)&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="36" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c36"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>5</mn><mn>6</mn></mfrac></math></mjx-assistive-mml></mjx-container> và&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="37" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c38"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>3</mn><mn>8</mn></mfrac></math></mjx-assistive-mml></mjx-container>.</p> <h4>3.Tìm các phân số bằng nhau trong các phân số dưới đây:</h4> <p><mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="38" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>2</mn><mn>5</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp;&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="39" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c34"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c37"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>4</mn><mn>7</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp; <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="40" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>12</mn><mn>30</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp;&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="41" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c32"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c32"></mjx-c><mjx-c class="mjx-c31"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>12</mn><mn>21</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp;&nbsp;<mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="42" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c32"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c33"></mjx-c><mjx-c class="mjx-c35"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>20</mn><mn>35</mn></mfrac></math></mjx-assistive-mml></mjx-container>;&nbsp; &nbsp; &nbsp; <mjx-container class="MathJax CtxtMenu_Attached_0" jax="CHTML" tabindex="0" ctxtmenu_counter="43" style="font-size: 116.7%; position: relative;"><mjx-math class="MJX-TEX" aria-hidden="true"><mjx-mfrac><mjx-frac><mjx-num><mjx-nstrut></mjx-nstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c34"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-num><mjx-dbox><mjx-dtable><mjx-line></mjx-line><mjx-row><mjx-den><mjx-dstrut></mjx-dstrut><mjx-mn class="mjx-n" size="s"><mjx-c class="mjx-c31"></mjx-c><mjx-c class="mjx-c30"></mjx-c><mjx-c class="mjx-c30"></mjx-c></mjx-mn></mjx-den></mjx-row></mjx-dtable></mjx-dbox></mjx-frac></mjx-mfrac></mjx-math><mjx-assistive-mml unselectable="on" display="inline"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>40</mn><mn>100</mn></mfrac></math></mjx-assistive-mml></mjx-container>.</p> <p style="text-align: center;"><img src="/uploads/tinymce/c1on-tap-1665843734.PNG.webp" width="254" height="400" alt="hinh-anh-on-tap-tinh-chat-co-ban-cua-phan-so-1571-0" title="hinh-anh-on-tap-tinh-chat-co-ban-cua-phan-so-1571-0" loading="lazy"></p><div> <div class="ads-horizontal-wrapped" style="height: auto !important; 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