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95
MCQ (Single Correct Answer)

The value of $c$ in Rolle's theorem for the function $f(x)=x^3-3 x$ in the interval $[0, \sqrt{3}]$ is

A
$1$
B
$-1$
C
$\frac{3}{2}$
D
$\frac{1}{3}$
96
MCQ (Single Correct Answer)

For the function $f(x)=x+\frac{1}{x}, x \in[1,3]$, the value of $c$ for mean value theorem is

A
1
B
$\sqrt3$
C
2
D
None of these
97

An example of a function which is continuous everywhere but fails to be differentiable exactly at two points is ............. .

Explanation

$|x|+|x-1|$ is continuous everywhere but fails to be differentiable exactly at two points $x=0$ and $x=1$.

So, there can be more such examples of functions.

98

Derivative of $x^2$ w.r.t. $x^3$ is ............. .

Explanation

Derivative of $x^2$ w.r.t. $x^3$ is $\frac{2}{3 x}$.

Let $$u=x^2 \text { and } v=x^3$$

$$\begin{array}{ll} \therefore & \frac{d u}{d x}=2 x \text { and } \frac{d v}{d x}=3 x^2 \\ \Rightarrow & \frac{d u}{d v}=\frac{2 x}{3 x^2}=\frac{2}{3 x} \end{array}$$

99

If $f(x)=|\cos x|$, then $f^{\prime}\left(\frac{\pi}{4}\right)$ is equal to ............ .

Explanation

If $f(x)=|\cos x|$, then $f^{\prime}\left(\frac{\pi}{4}\right)$

$\because \quad 0< x<\frac{\pi}{2}, \cos x>0$.

$$\begin{array}{l} \therefore & f(x) & =+\cos x & \\ \Rightarrow & f^{\prime}(x) & =(-\sin x) \\ \Rightarrow & f^{\prime}\left(\frac{\pi}{4}\right) & =-\sin \frac{\pi}{4}=\frac{-1}{\sqrt{2}} & {\left[\because \sin \frac{\pi}{4}=\frac{1}{\sqrt{2}}\right]} \end{array}$$