$$\frac{5b+(a+b)^{2}}{(a-b)^{2}}$$
$\frac{f\left(a^{2}+2ab+b^{2}+5b\right)}{\left(a-b\right)^{2}}$
$\frac{2abf+5bf+fa^{2}+fb^{2}}{\left(a-b\right)^{2}}$
