a) $(\frac{3}{7})^{5} \times x = (\frac{3}{7})^{7}$
$ x = (\frac{3}{7})^{7} / (\frac{3}{7})^{5}$
$x= (\frac{3}{7})^{2}$
$x = \frac{9}{49}$
Vậy $x = \frac{9}{49}$.
b) $(0.09)^{3} / x = -(0.09)^{2}$
$x = (0.09)^{3} / [-(0.09)^{2}]$
$x = -[(0.09)^{3} / (0.09)^{2}]$
x = -0.09
Vậy x = -0.09