Having a bit of trouble with this one. Can anyone help me out?

Many thanks.

Q.Find the second derivative of $\displaystyle y=\sqrt{2x+3}$.

Attempt:$\displaystyle y=(2x+3)^{1/2}$

$\displaystyle f'(x)=(1/2)(2x+3)^{-1/2}(2)\rightarrow \frac{1}{\sqrt{2x+3}}$

$\displaystyle f''(x)=(-1/2)(2x+3)^{-3/2}(2)\rightarrow -\frac{1}{\sqrt{(2x+3)^3}}$

Ans:(From text book): $\displaystyle \frac{-1}{2\sqrt{(2x+3)^3}}$