2) (-\frac{5m^{4}}{6n^{6}})^{3}.

2) $$\left(-\frac{5m^{4}}{6n^{6}}\right)^{3}=-\frac{(5m^{4})^{3}}{(6n^{6})^{3}}=-\frac{5^{3}m^{12}}{6^{3}n^{18}}=-\frac{125m^{12}}{216n^{18}}$$

Ответ: $$\frac{-125m^{12}}{216n^{18}}$$