\[\left( m^{2} - n \right)\left( m + n^{2} \right) =\]
\[= m^{2} \cdot m + m^{2}n^{2} - n \cdot m - n \cdot n^{2} =\]
\[= m^{2 + 1} + m^{2}n^{2} - mn - n^{1 + 2} =\]
\[= m^{3} + m^{2}n^{2} - mn - n^{3}\text{.\ }\]