Question

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

• A. $3x + 4$
• B. $f(x) = y.$
• C. $\frac{1}{3}(x + 4)$
• D. $\frac{1}{3}(x - 4)$

Answer 1

Answer: (C)

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

Answer 2

$f(x) = 3x - 4 = y$ $\Rightarrow$ $y = 3x - 4$ $\Rightarrow$ $x = \frac{y + 4}{3}$

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