Jambmaths question:
The inverse of the function $f(x)=3x+4$ is
Option A:
$\tfrac{1}{3}(x-4)$
Option B:
$\tfrac{1}{5}(x-5)$
Option C:
$\tfrac{1}{4}(x+3)$
Option D:
$\tfrac{1}{3}(x+4)$
Jamb Maths Solution:
$\begin{align} & f(x)=3x+4 \\ & Let\text{ }y=3x+4 \\ & 3x=f(x)-4 \\ & x=\tfrac{1}{3}[f(x)-4] \\ & \text{Now replace back }f(x)\text{ with }x\text{ and }x\text{ with }{{f}^{-1}}(x) \\ & {{f}^{-1}}(x)=\tfrac{1}{3}(x-4)\text{ }\!\!\{\!\!\text{ Where }{{f}^{-1}}(x)\text{ is the inverse }f(x)\} \\\end{align}$
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