Practicing Success
Let $f(x)=|x|+|\sin x|, x \in(-\pi / 2, \pi / 2)$. Then, |
nowhere continuous continuous and differentiable everywhere nowhere differentiable differentiable everywhere except at x = 0 |
differentiable everywhere except at x = 0 |
We have, $f(x) =|x|+|\sin x|$ for all $x \in(-\pi / 2, \pi / 2)$ $\Rightarrow f(x) = \begin{cases}-x-\sin x & \text { for }-\pi / 2<x<0 \\ x+\sin x & \text { for } 0 \leq x<\pi / 2\end{cases}$ Clearly, $\lim\limits_{x \rightarrow 0^{-}} f(x)=f(0)=\lim\limits_{x \rightarrow 0^{+}} f(x)$ So, f(x) is continuous at x = 0 Also, f(x) is continuous on $(-\pi / 2,0) \cup(0, \pi / 2)$. Thus, f(x) is continuous on $(-\pi / 2, \pi / 2)$ Now, (LHD at x = 0) $=\left\{\frac{d}{d x}(-x-\sin x)\right\}_{\text {at } x=0}=\{-1-\cos x\}_{\text {at } x=0}=-1-1=-2$ and, (RHD at x = 0) $=\left\{\frac{d}{d x}(x+\sin x)\right\}_{\text {at } x=0}=\{1+\cos x\}_{\text {at } x=0}=1+1=2$ Clearly, (LHD at x = 0) ≠ (RHD at x = 0) Clearly, f(x) is differentiable on $(-\pi / 2,0) \cup(0, \pi / 2)$. Hence, f(x) is everywhere differentiable except at x = 0 |