Draw A Reuleaux Triangle!
JavaScript + HTML, 164 158 + 13 = 171 bytes



w=+prompt(f=(x,y)=&gt;x*x+y*y&lt;w*w);C.width=C.height=w*2;for(y=-w;++y&lt;w;)for(x=-w;++x&lt;w;)f(x,y)&amp;f(w-x,y)&amp;f(w/2-x,y-w*.866)&amp;&amp;C.getContext`2d`.fillRect(x+w,y+w,1,1)
&lt;canvas id=C&gt;




I don't know why I enjoy answering these mathy drawing challenges with &lt;canvas&gt; so much...