$7.4 

$a.$ $\frac{a^2+ab}{b-a}$ :  $\frac{a+b}{2a^2-2b^2}$ .
= $\frac{a^2+ab}{b-a}$ .  $\frac{2a^2-2b^2}{a+b}$ .
= $\frac{(a^2+ab)(2a^2-2b^2)}{(b-a)(a+b)}$ .
= $\frac{-2a(a+b)(a+b)(a-b)}{(a-b)(a+b)}$ .
= $-2a(a+b).$

$b.$ $\frac{5x-15}{4x+4}$ :  $\frac{x^2-9}{x^2+2x+1}$ .
=  $\frac{5x-15}{4x+4}$ .  $\frac{x^2+2x+1}{x^2-9}$ .
= $\frac{(5x-15)(x^2+2x+1)}{(4x+4)(x^2-9)}$ .
= $\frac{5(x-3)(x+1)^2}{4(x+1)(x-3)(x+3)}$ .
= $\frac{5(x+1)}{4(x+3)}$ .

(Sai sót chỗ nào ới mình nhé).

_Chúc bạn học tốt_

user0034, luv q.