# How do you simplify ab(b^2-0.4a^2b)?

To simplify this expression multiply each term within parenthesis by $\textcolor{red}{a b}$:
$\textcolor{red}{a b} \left({b}^{2} - 0.4 {a}^{2} b\right) = \left(\textcolor{red}{a b} \times {b}^{2}\right) - \left(\textcolor{red}{a b} \times 0.4 {a}^{2} b\right) =$
$a {b}^{3} - 0.4 {a}^{3} {b}^{2}$