Math Help - Second Derivatives

1. Second Derivatives

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

Many thanks.

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

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

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