$$\frac{a}{a^{2}-2ab+b^{2}}-\frac{b}{a^{2}-b^{2}}$$
$\frac{a^{2}+b^{2}}{\left(a+b\right)\left(a-b\right)^{2}}$
$\frac{-a^{3}-5ab^{2}-b^{3}-ba^{2}}{\left(a+b\right)^{2}\left(a-b\right)^{3}}$
