Jambmaths question:
If $y=3\sin (-4x)$ ,$\tfrac{dy}{dx}$ is
Option A:
$-12x\cos (-4x)$
Option B:
$12x\cos (4x)$
Option C:
$12\sin (-4x)$
Option D:
$-12\cos (-4x)$
Jamb Maths Solution:
$\begin{align} & y=3\sin (-4x) \\ & \text{Let }u=-4x,\text{ }y=3\sin u \\ & \frac{dy}{du}=3\cos u,\text{ }\frac{du}{dx}=-4 \\ & \frac{dy}{dx}=\frac{dy}{du}\times \frac{du}{dx}=3\cos u\times (-4) \\ & \frac{dy}{dx}=-12\cos u=-12\cos (-4x) \\\end{align}$
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