Simplify:
a^2-b^2=(a-b)(a+b); a^2-2ab+b^2=(a-b)^2; 4a^2-b^2=(2a-b)(2a+b).
Simplify the divisor: (a-b)^3/((2a-b)(2a+b)(a+b))
To divide by a fraction, invert it and multiply:
((a-b)(a+b)/(2a-b))((2a-b)(2a+b)(a+b)/(a-b)^3)=
(a-b)(a+b)(2a-b)(2a+b)(a+b)/((2a-b)(a-b)^32)=
((a+b)^2)(2a+b)/(a-b)^2 or (2a+b)((a+b)/(a-b))^2.