2.
(a-2b)/(b²-a²)=(a-2b)/((b-a)(b+a))=-(a-2b)/((a-b)(a+b))=(2b-a)/((a-b)*(a+b))=
=4*(2b-a)/(4*(a-b)*(a+b))=(8b-4a)/((4a-4b)(a+b)).
5b/(4a-4b)=5b*(a+b)/((4a-4b)(a+b)).
3.
(2x+8y)/(x²-16y²)=2*(x+4y)/((x+4y)(x-4y))= 2/(x-4y)=-2/(4y-x)=-2/(1/5)=-2*5=-10.