Question

If $\cos c=\frac{\sin (2\pi +\frac{\pi }{2})-\sin \pi /2}{\pi }$, find the value of $c$.

Answer 1

$\sin (2\pi +\theta )=\sin \theta$

$\therefore \cos c=\frac{\sin \pi /2-\sin \pi /2}{\pi }=0$

$c={\cos }^{-1}\left(0\right)=\pi /2$