\[\left( \frac{a}{b} \right)^{3} - \left( \frac{c}{d} \right)^{3} =\]
\[= \left( \frac{a}{b} - \frac{c}{d} \right)\left( \frac{a^{2}}{b^{2}} + \frac{\text{ac}}{\text{bd}} + \frac{c^{2}}{d^{2}} \right) =\]
\[= \frac{ad - bc}{\text{bd}} \cdot \frac{a^{2}d^{2} + abcd + c^{2}b^{2}}{b^{2}d^{2}} \Longrightarrow\]
\[\Longrightarrow да,\ верно.\]