\(\displaystyle \frac{2-\sqrt{4+h}}{h\sqrt{4+h}}\)

\(\displaystyle =\frac{2-\sqrt{4+h}}{h\sqrt{4+h}}\left(\frac{2+\sqrt{4+h}}{2+\sqrt{4+h}}\right)\)

\(\displaystyle =\frac{-h}{h\sqrt{4+h}\left(2+\sqrt{4+h}\right)}\)

\(\displaystyle =\frac{-1}{\sqrt{4+h}\left(2+\sqrt{4+h}\right)}\)