If ab = 5 and a² + b² = 25, then (a + b)² =

35
Explanation:
Recall that (a+b)^2=a^2+2ab+b^2.
We can rearrange it in a way that would make it easier to solve our problem:
(a^2+b^2)+2ab
Now, we just plug in 25 for a^2+b^2, and plug in 5 for ab:
25+2*5
=25+10
=35