JAMB 2017 · UTME (set 2) · Q7

If $y = x\sin x$ , find $\dfrac{dy}{dx}$ when $x = \dfrac{\pi}{2}$ .

Worked solution (try it first)

Product rule: $\frac{dy}{dx} = \sin x + x\cos x$ .
At $x = \frac\pi2$ , $\sin x = 1$ and $\cos x = 0$ , so $\frac{dy}{dx} = 1 + 0 = 1$ , option C.