JAMB 2003 · UME · Q37

If $y = 3\sin(-4x)$ , then $\frac{dy}{dx}$ is

Worked solution (try it first)

Chain rule: $\sin(-4x)$ differentiates to $\cos(-4x)$ times the derivative of $-4x$ , which is $-4$ .
So $\frac{dy}{dx} = 3 \times (-4)\cos(-4x)$
$= -12\cos(-4x)$ , option A.