The points on the curve  $y=\sin x$, where the tangent is parallel to the x-axis is

$\begin{array}{rl} & y=\sin x\\ & \frac{dy}{dx}=\cos x\end{array}$
Tangent line parallel to x-axis
$\cos x=0$
$\begin{array}{rl} & x=(2n+1)\left(\frac{\pi }{2}\right)n\in Z\\ & n=0,x=\pi /2\text{then}y=\sin 90\\ & \Rightarrow y=1\\ & n=1,x=\frac{3\pi }{2},\text{then}y=-1\\ & (\therefore (2n+1\left)\frac{\pi }{2}(-1^n)\right)n\in Z\end{array}$