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If F ( X ) = Log ( 1 + X 1 − X ) and G ( X ) = 3 X + X 3 1 + 3 X 2 , Then F(G(X)) is Equal To(A) F(3x) (B) {F(X)}3 (C) 3f(X) (D) −F(X - Mathematics

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प्रश्न

If  \[f\left( x \right) = \log \left( \frac{1 + x}{1 - x} \right) \text{ and}  g\left( x \right) = \frac{3x + x^3}{1 + 3 x^2}\] , then f(g(x)) is equal to

 

विकल्प

  • (a) f(3x)

  • (b) {f(x)}3

  • (c) 3f(x)

  • (d) −f(x)

     
MCQ

उत्तर

(c) 3f(x)

\[f\left( x \right) = \log \left( \frac{1 + x}{1 - x} \right) \text{ and } g\left( x \right) = \frac{3x + x^3}{1 + 3 x^2}\] \[Now, \]
\[\frac{1 + g(x)}{1 - g(x)} = \frac{1 + \frac{3x + x^3}{1 + 3 x^2}}{1 - \frac{3x + x^3}{1 + 3 x^2}}\]
\[ = \frac{1 + 3 x^2 + 3x + x^3}{1 + 3 x^2 - 3x - x^3}\]
\[ = \frac{(1 + x )^3}{(1 - x )^3}\]
\[\text{ Then } , f(g(x)) = \log \left( \frac{1 + g(x)}{1 - g(x)} \right)\]
\[ = \log \left( \frac{1 + x}{1 - x} \right)^3 \]
\[ = 3 \log \left( \frac{1 + x}{1 - x} \right)\]
\[ = 3f(x))\]

 

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अध्याय 3: Functions - Exercise 3.6 [पृष्ठ ४३]

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आरडी शर्मा Mathematics [English] Class 11
अध्याय 3 Functions
Exercise 3.6 | Q 9 | पृष्ठ ४३

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