Question
Choose the correct answer from the given four options.

Let f : R → R be the functions defined by f(x) = x3 + 5. Then f-1(x) is:

  1. $(\text{x}+5)^\frac{1}{3}$

  2. $(\text{x}-5)^\frac{1}{3}$

  3. $(5-\text{x})^\frac{1}{3}$

  4. $5-\text{x}$

Answer

  1. $(\text{x}-5)^\frac{1}{3}$

Solution:

we are given that, $\text{f}(\text{x})=\text{x}^3 +5$

Let us suppose, $\text{y}=\text{x}^3+5$

$\Rightarrow\ \text{x}^3=\text{y}-5$

$\Rightarrow\text{x}=(\text{y}-5)^{\frac{1}{3}}$

$\begin{bmatrix}\because\text{f}(\text{x})=\text{y}\\\Rightarrow\text{x}=\text{f}^{-1}(\text{y})\end{bmatrix}$

$\Rightarrow\text{f}^{-3}(\text{y})=(\text{y}-5)^{\frac{1}{3}}$

$\Rightarrow\text{f}^{-1}(\text{x})=(\text{x}-5)^{\frac{1}{3}}$

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