For example, Say we have the number 10.
[1+9 = 10] , 1\*9 = 9
[2+8 = 10] , 2\*8 = 16
[3+7 = 10] , 3\*7 = 21
[4+6 = 10] , 4\*6 = 24
[5+5 = 10] , 5\*5 = 25  

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10+0 = 10

I want to know how to show that two different numbers 
 that their sum that adds up to 10. say (3,7) and (4,6) their products will 
 always be different. How can I show this in a general case? I trying to get  

 better with proofs