ПОМОГИТЕ ЗА 40 БАЛЛОВ

Решите задачу:

$\frac{a}{a-b}-\frac{a+b}{a-b} = \frac{a-a-b}{a-b}=\frac{-b}{a-b} = \frac{b}{b-a}$

$\frac{a}{a-b}-\frac{a+b}{b-a} = \frac{a}{a-b}+\frac{a+b}{a-b} = \frac{2a+b}{a-b}$

$\frac{a}{a-b}+\frac{a+b}{2a-2b} = \frac{a}{a-b}+\frac{a+b}{2(a-b)} = \frac{2a+a+b}{2(a-b)} = \frac{3a+b}{2(a-b)}$

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

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

$\frac{a}{a-b}-\frac{ab(a+b)}{a^3-b^3} = \frac{a}{a-b}-\frac{ab(a+b)}{(a-b)(a^2+ab+b^2)} = \frac{a(a^2+ab+b^2)-ab(a+b)}{(a-b)(a^2+ab+b^2)} = \\\\ =\frac{a^3+a^2b+ab^2-a^2b-ab^2}{(a-b)(a^2+ab+b^2)} = \frac{a^3}{(a-b)(a^2+ab+b^2)}$