\[\left( \frac{2}{3}a^{2}b \right)^{2} = \left( \frac{2}{3} \right)^{2}\left( a^{2}b^{2} \right) =\]
\[= \frac{4}{9}a^{4}b^{2} \Longrightarrow коэффициент\ \frac{4}{9};\ \ \]
\[степень\ \ 6.\]