Rewrite the square root of the division $\frac{81}{16}$ as the division of square roots $\frac{\sqrt{81}}{\sqrt{16}}$. Take the square root of both numerator and denominator.
$$\sqrt{\frac{9}{4}}$$
Rewrite the square root of the division $\frac{9}{4}$ as the division of square roots $\frac{\sqrt{9}}{\sqrt{4}}$. Take the square root of both numerator and denominator.
