मराठी

Verify Lagrange'S Mean Value Theorem for the Following Function on the Indicated Intervals. Find a Point 'C' in the Indicated Interval as Stated by the Lagrange'S F ( X ) = X + 1 X on [ 1 , 3 ] - Mathematics

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प्रश्न

Verify Lagrange's mean value theorem for the following function on the indicated intervals. find a point 'c' in the indicated interval as stated by the Lagrange's mean value theorem \[f\left( x \right) = x + \frac{1}{x} \text { on }[1, 3]\] ?

बेरीज

उत्तर

 We have,

\[f\left( x \right) = x + \frac{1}{x} = \frac{x^2 + 1}{x}\]

Clearly,  \[f\left( x \right)\] is continuous on \[\left[ 1, 3 \right]\] and derivable on \[\left( 1, 3 \right)\]

Thus, both the conditions of lagrange's theorem are satisfied.
Consequently, there exists some  \[c \in \left( 1, 3 \right)\] such that \[f'\left( c \right) = \frac{f\left( 3 \right) - f\left( 1 \right)}{3 - 1} = \frac{f\left( 3 \right) - f\left( 1 \right)}{2}\]

Now, \[f\left( x \right) = \frac{x^2 + 1}{x}\]\[f'\left( x \right) = \frac{x^2 - 1}{x^2}\]\[f\left( 1 \right) = 2\],\[f\left( 3 \right) = \frac{10}{3}\]

∴\[f'\left( x \right) = \frac{f\left( 3 \right) - f\left( 1 \right)}{2}\]

\[\Rightarrow \frac{x^2 - 1}{x^2} = \frac{4}{6}\]

\[ \Rightarrow \frac{x^2 - 1}{x^2} = \frac{2}{3}\]

\[ \Rightarrow 3 x^2 - 3 = 2 x^2 \]

\[ \Rightarrow x = \pm \sqrt{3}\]

Thus, \[c = \sqrt{3} \in \left( 1, 3 \right)\] such that 

\[f'\left( c \right) = \frac{f\left( 3 \right) - f\left( 1 \right)}{3 - 1}\] .
Hence, Lagrange's theorem is verified.
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पाठ 15: Mean Value Theorems - Exercise 15.2 [पृष्ठ १७]

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आरडी शर्मा Mathematics [English] Class 12
पाठ 15 Mean Value Theorems
Exercise 15.2 | Q 1.11 | पृष्ठ १७

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