1. ## [SOLVED] Derivative

$y=2cos(\frac {x}{2})$, $\frac {d^2y}{dx^2}$

any hints were to begin

2. First find the first derivative via chain rule:
$\begin{array}{rcl}\displaystyle \frac{dy}{dx} & = & \displaystyle -2\sin \left(\frac{x}{2}\right) \cdot \left(\frac{x}{2}\right)' \\ & = & \displaystyle -2\sin \left(\frac{x}{2}\right) \cdot \frac{1}{2} \\ & = & \displaystyle -\sin \left(\frac{x}{2}\right) \end{array}$

Now apply the chain rule again to find the second derivative.

3. Got it now the fraction was messing me

thank you

-1/2cos(x/2)