When we want to calculate the root of a fraction, we need to find a number that is equal to this fraction when squared. For $\sqrt{\green{\tfrac{4}{9}}}$, we are looking for a number that, when squared, equals $\green{\tfrac{4}{9}}$. This is $\blue{\tfrac{2}{3}}$ because $$\left(\blue{\frac{2}{3}}\right)^2=\frac{\blue2^2}{\blue3^2}=\green{\frac{4}{9}}$$

We can therefore see that:

$$\sqrt{\green{\frac{4}{9}}}=\frac{\sqrt{\green4}}{\sqrt{\green9}}=\blue{\frac{2}{3}}$$

In general, we can state:

The square root of a fraction is equal to the square root of the numerator divided by the square root of the denominator.

Examples

$$\begin{array}{rcl}\displaystyle \sqrt{\green{\frac{1}{4}}}&=&\displaystyle \frac{\sqrt{\green1}}{\sqrt{\green4}} \\ &=& \displaystyle \blue{\frac{1}{2}} \\ \\ \displaystyle \sqrt{\green{\frac{3}{4}}}&=&\displaystyle \frac{\sqrt{\green3}}{\sqrt{\green4}} \\ &=& \displaystyle \frac{\blue{\sqrt{3}}}{\blue2} \\ \\ \displaystyle \sqrt{\green{\frac{2}{3}}}&=&\displaystyle \frac{\blue{\sqrt{2}}}{\blue{\sqrt{3}}} \end{array}$$