Упростить выражение ,(которые помечены галочкой )

Решите задачу:

$\frac{mn^4-an^4}{an^3-mn^3}+2n = \frac{n^4(m-a)}{n^3(a-m)} +2n=- \frac{n^4(m-a)}{n^3(m-a)}+2n=-n+2n=n$

$\frac{x^4-y^4}{x^3+yx^2-xy^2-y^3}-2y= \frac{x^2-y^2)(x^2+y^2)}{(x^3+x^2y)-(xy^2+y^3)}-2y=\\\\ \frac{(x-y)(x+y)(x^2+y^2)}{x^2(x+y)-y^2(x+y)}-2y= \frac{(x-y)(x+y)(x^2+y^2)}{(x^2-y^2)(x+y)}-2y=\\\\ = \frac{(x-y)(x+y)(x^2+y^2)}{(x-y)(x+y)(x+y)}-2y= \frac{x^2+y^2}{x+y}-2y=\\\\ = \frac{x^2+y^2-2y(x+y)}{x+y}= \frac{x^2+y^2-2xy-2y^2}{x+y}= \frac{x^2-2xy-y^2}{x+y}$