\[\boxed{\mathbf{2.521}\mathbf{.\ ОК\ ГДЗ - домашка\ на\ }5}\]
\[\textbf{а)}\ \left( \frac{2}{3}\ :\frac{4}{9} \right)^{2} = \left( \frac{2}{3} \cdot \frac{9}{4} \right)^{2} = \left( \frac{3}{2} \right)^{2} =\]
\[= \frac{9}{4} = 2\frac{1}{4}\ \]
\[\textbf{б)}\ \left( \frac{2}{3} \right)^{2}\ :\left( \frac{4}{9} \right)^{2} = \frac{4}{9}\ :\frac{16}{81} =\]
\[= \frac{4}{9} \cdot \frac{81}{16} = \frac{9}{4} = 2\frac{1}{4}\]
\[\textbf{в)}\ \left( \frac{2}{9} \cdot \frac{7}{8}\ :\frac{7}{18} \right)^{3} = \left( \frac{2}{9} \cdot \frac{7}{8} \cdot \frac{18}{7} \right)^{3} =\]
\[= \left( \frac{1}{2} \right)^{3} = \frac{1}{8}\ \]