I have no idea how to solve this..can somebody give me some help? thanks
Expand $\displaystyle \cos(\pi/2+h)$ using the multiple angle formula:
$\displaystyle
\frac{\cos(\pi/2+h)-\cos(\pi/2)}{h}=\frac{\cos(\pi/2)\cos(h)-\sin(\pi/2)\sin(h)-\cos(\pi/2)}{h}
$
........... $\displaystyle =\frac{\cos(\pi/2)(\cos(h)-1)-\sin(\pi/2)\sin(h)}{h}
$
........... $\displaystyle =\frac{\cos(\pi/2)(\cos(h)-1)}{h}-\frac{\sin(\pi/2)\sin(h)}{h}
$
The limit of the first term above is $\displaystyle 0$, and the second is $\displaystyle -\sin(\pi/2)$
RonL