Simplifying square root with fraction I'm not sure about this equality $$4(-3+\sqrt {15})/4)^2 = (9-6 \sqrt{15} +15)/4$$ 
Hope some one can enlighten me. I will be facing more of such fractions, please guide me on how to solve/simplify in easy method.
Thanks :)

I’ll even finish the simplification:
$$\begin{align*}
4\left(\frac{-3+\sqrt{15}}4\right)^2&=4\cdot\frac{(-3+\sqrt{15})(-3+\sqrt{15}}{4\cdot4}\\
&=\frac{(-3)^2+2(-3)\sqrt{15}+(\sqrt{15})^2}4\\
&=\frac{9-6\sqrt{15}+15}4\\
&=\frac{24-6\sqrt{15}}4\\
&=6-\frac32\sqrt{15}\;.
\end{align*}$$
In short: cancel a factor of $4$, and multiply out the numerator.
