Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Continuity and Differentiability

Question:

Rolle's theorem is not applicable to the function $f(x)=|x|$ for $-2 \leq x \leq 2$ because

Options:

$f$ is continuous on $[-2,2]$

$f$ is not differentiable at $x=0$

$f(-2)=f(x)$

$f$ is not a constant function

Correct Answer:

$f$ is not differentiable at $x=0$

Explanation:

We have,

$f(x)=|x|= \begin{cases}x, & x \geq 0 \\ -x, & x<0\end{cases}$

∴  (LHD at x = 0) = $\lim\limits_{x \rightarrow 0^{-}} \frac{f(x)-f(0)}{x-0}=\lim\limits_{x \rightarrow 0^{-}} \frac{-x-0}{x-0}=-1$

and, (RHD at x = 0) = $\lim\limits_{x \rightarrow 0^{+}} \frac{f(x)-f(0)}{x-0}=\lim\limits_{x \rightarrow 0^{+}} \frac{x-0}{x-0}=1$

∴  (LHD at x = 0) ≠ (RHD at x = 0)

So, f(x) is not differentiable at x = 0.

Consequently, Rolle's is not applicable to the given function.