a: \(\frac{4m^2-8mn}{5\left(2n-m\right)^3}\)
\(=\frac{4m\left(m-2n\right)}{5\left(2n-m\right)^3}\)
\(=\frac{-4m\left(2n-m\right)}{5\left(2n-m\right)^3}=\frac{-4m}{5\left(2n-m\right)^2}\)
b: \(\frac{9-\left(b+2\right)^2}{b^2+10b+25}\)
\(=\frac{\left(3-b-2\right)\left(3+b+2\right)}{\left(b+5\right)^2}=\frac{\left(1-b\right)\left(b+5\right)}{\left(b+5\right)^2}\)
\(=\frac{1-b}{b+5}\)


