3)mn = m³n².

3) $$ \frac{5}{6} m^5n^4 = \frac{1}{3}m^3n^2 \cdot \textbf{\frac{5}{2}m$$^{2}$$n$$^{2}$$}$$

Ответ: $$\frac{5}{2}m^{2}n^{2}$$