algebra precalculus - How does $frac12sqrt{n^2 + frac{4m^3}{27}}$ become $sqrt{frac{n^2}4 + frac{m^3}{27}}$?

$$\begin{align} &\frac n2 \pm \frac12 \,\sqrt{n^2 + \frac{4m^3}{27}}\\[6pt] =\; &\frac n2 \pm \phantom{\frac12}\sqrt{\frac{n^2}4 + \frac{m^3}{27}} \end{align}$$

Can someone please explain me how this radical multiplied by $1/2$ becomes this? You can see $1/2$ disappeared, and division by $4$ appeared under square root.

Thanks.