Question

Let $f:R\to R$ be defined by $f\left(x\right)=3x-4$ then $f^{-1}\left(x\right)$ is

• A. $\frac{1}{3}(x+4)$
• B. $\frac{1}{3}(x-4)$
• C. $3x+4$
• D. not defined

Answer 1

Answer: (A)

$\frac{1}{3}(x+4)$

$f\left(x\right)$ is invertible for all real values of $x$
Hence

$y=3x-4$
$y+4=3x$
$\frac{y+4}{3}=x$
$f^{-1}\left(x\right)=\frac{x+4}{3}$