\[\boxed{\text{279\ (279).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ 81m^{4}n^{16} =\]
\[= - \frac{1}{3}mn^{14} \cdot ( - 243m^{3}n^{2})\]
\[2)\ 81m^{4}n^{16} =\]
\[= \left( 9m^{2}n^{8} \right)^{2}\ или\ \ \left( \ - 9m^{2}n^{8} \right)^{2}\]
\[3)\ 81m^{4}n^{16} =\]
\[= \left( 3mn^{4} \right)^{4}\ \ или\ \left( - 3mn^{4} \right)^{4}\]