\(\boxed{\mathbf{3.39}\mathbf{.\ ОК\ ГДЗ - домашка\ на\ }5}\)
Пояснение.
Решение.
\[\textbf{а)}\ \frac{8}{7} = \frac{4}{3,5}\]
\[7 \cdot 4 = 3,5 \cdot 8\]
\[7 \cdot 4 = 28\]
\[8 \cdot 3,5 = 28\]
\[\textbf{б)}\ 0,6\ :\frac{2}{3} = 21\ :23\frac{1}{3}\]
\[\frac{2}{3} \cdot 21 = 0,6 \cdot 23\frac{1}{3}\]
\[\frac{2}{3} \cdot 21 = 2 \cdot 7 = 14\]
\[0,6 \cdot 23\frac{1}{3} = \frac{6}{10} \cdot \frac{70}{3} = 2 \cdot 7 = 14\]
\[\textbf{в)}\ \frac{2}{9}\ :0,2 = 17\ :15,3\]
\[0,2 \cdot 17 = \frac{2}{9} \cdot 15,3\]
\[0,2 \cdot 17 = 3,4\]
\[\frac{2}{9} \cdot \frac{153}{10} = \frac{17}{5} = 3,4\]
\[Все\ равенства\ верные.\]