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Need solution for RD Sharma maths class 12 chapter 10 Differentiation exercise Multiple choice question 23

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Answer:

        None of these

Hint:

        In case of function of one variable it’s a function that doesn’t have finite derivation

Given:

        f(x)=\sqrt{x^{2}-10 x+25}, f^{\prime}(x)=

Solution:  

        f(x)=\sqrt{x^{2}-10 x+25}

                  \begin{aligned} &=\sqrt{(x-5)^{2}} \\\\ &=|x-5| \end{aligned}

f(x)=\left\{\begin{array}{cll} x-5 & \text { for } & x>5 \\\\ -(x-5) & \text { for } & x<5 \end{array}\right.

L H D=\lim _{x \rightarrow 5^{-}} \frac{f(x)-f(a)}{x-a}

            =\lim _{x \rightarrow 5^{-}} \frac{\sqrt{x^{2}-10 x+25}-\sqrt{5^{2}-10(5)+25}}{x-5}

            =\lim _{x \rightarrow 5^{-}} \frac{|x-5|}{(x-5)}=\lim _{x \rightarrow 5^{-}} \frac{-(x-5)}{x-5}=-1

R H D=\lim _{x \rightarrow 5^{+}} \frac{f(x)-f(a)}{x-a}

            =\lim _{x \rightarrow 5^{+}} \frac{\sqrt{x^{2}-10 x+25}-\sqrt{5^{2}-10(5)+25}}{x-5}

            \begin{aligned} &=\lim _{x \rightarrow 5^{+}} \frac{|x-5|}{x-5} \\\\ &=\lim _{x \rightarrow 5^{+}} \frac{x-5}{x-5} \\\\ &=1 \end{aligned}

L H D \neq R H D, so function is not differentiable .

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