\[3a^{3}b - 6a^{2}b^{2} =\]
\[= 3a^{2}b\left( a^{3 - 2} - \frac{6}{3}b^{2 - 1} \right) =\]
\[= 3a^{2}b(a - 2b)\]
\[Проверка:\]
\[3a^{2}b(a - 2b) =\]
\[= 3a^{2 + 1}b - 6a^{2}b^{1 + 1} =\]
\[= 3a^{3}b - 6a^{2}b^{2}\ ;\]
\[3a^{3}b - 6a^{2}b^{2} = 3a^{3}b - 6a^{2}b^{2}\]
\[верно.\]