Jambmaths question:
Differentiate (2x + 5)2 (x – 4) with respect to x
Option A:
4(2x+5)(x – 4)
Option B:
4(2x + 5)((4x – 3)
Option C:
(2x +5)(2x – 13)
Option D:
(2x + 5)(6x – 11)
Jamb Maths Solution:
$\begin{align} & y={{(2x+5)}^{2}}(x-4) \\ & y=uv\text{ (where }u\text{ and }v\text{ are function of }x) \\ & \frac{dy}{dx}=u\frac{dv}{dx}+v\frac{du}{dx} \\ & u={{(2x+5)}^{2}},\text{ }\frac{du}{dx}=2(2x+5)\times 2=4(2x+5) \\ & v=(x-4),\text{ }\frac{dv}{dx}=1 \\ & \frac{dy}{dx}=u\frac{dv}{dx}+v\frac{du}{dx} \\ & \frac{dy}{dx}={{(2x+5)}^{2}}\cdot 1+(x-4)[4(2x+5)] \\ & \frac{dy}{dx}={{(2x+5)}^{2}}+4(x-4)(2x+5) \\ & \frac{dy}{dx}=(2x+5)\left[ 2x+5+4(x-4) \right] \\ & \frac{dy}{dx}=(2x+5)\left[ 2x+5+4x-16 \right] \\ & \frac{dy}{dx}=(2x+5)(6x-11) \\\end{align}$
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