JAMB 1995 · UME · Q37

Which of the following is a sketch of $y = 3\sin x$ ?

Worked solution (try it first)

At $x = 0$ , $y = 3\sin 0 = 0$ , so the curve passes through the origin.
That rules out B and D.
At $x = \frac{\pi}{2}$ , $y = 3\sin\frac{\pi}{2} = 3$ , a maximum.
At $x = -\frac{\pi}{2}$ , $y = -3$ , a minimum.
Only sketch C rises through the origin to 3 at $\frac{\pi}{2}$ , so the answer is option C.