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Discuss the Applicability of Lagrange'S Mean Value Theorem for the Function F(X) = | X | on [−1, 1] ? - Mathematics

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Question

Discuss the applicability of Lagrange's mean value theorem for the function
f(x) = | x | on [−1, 1] ?

Sum
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Solution

Given:

\[f\left( x \right) = \left| x \right|\]

If Lagrange's theorem is applicable for the given function, then \[f\left( x \right)\] is continuous on \[\left[ - 1, 1 \right]\] and differentiable on \[\left( - 1, 1 \right)\] But it is known that \[f\left( x \right) = \left| x \right|\] is not differentiable at \[x = 0 \in \left( - 1, 1 \right)\] . 

Thus, our supposition is wrong.
Therefore, Lagrange's theorem is not applicable for the given function.

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Chapter 15: Mean Value Theorems - Exercise 15.2 [Page 18]

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RD Sharma Mathematics [English] Class 12
Chapter 15 Mean Value Theorems
Exercise 15.2 | Q 2 | Page 18

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