\[\left( m^{6} - n^{5} \right)\left( - m^{6} - n^{5} \right) =\]
\[= - \left( m^{6} - n^{5} \right)\left( m^{6} + n^{5} \right) =\]
\[= - \left( m^{12} - n^{10} \right) =\]
\[= n^{10} - m^{12}\]