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If F(X) = Cos (Log X), Then Value of F ( X ) F ( 4 ) − 1 2 { F ( X 4 ) + F ( 4 X ) } is (A) 1 (B) −1 (C) 0 (D) ±1 - Mathematics

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प्रश्न

If f(x) = cos (log x), then value of \[f\left( x \right) f\left( 4 \right) - \frac{1}{2} \left\{ f\left( \frac{x}{4} \right) + f\left( 4x \right) \right\}\] is 

विकल्प

  • (a) 1

  • (b) −1

  • (c) 0

  • (d) ±1

     
MCQ

उत्तर

(c) 0

Given : f(x) = cos (log x)
Then, \[f\left( x \right) f\left( 4 \right) - \frac{1}{2} \left\{ f\left( \frac{x}{4} \right) + f\left( 4x \right) \right\}\]

\[= \cos (\log x)\cos(\log 4) - \frac{1}{2}\left\{ \cos \left( \log\frac{x}{4} \right) + \cos\left( \log4x \right) \right\}\]
\[ = \frac{1}{2}\left[ \cos\left( \log x + \log 4 \right) + \cos \left( \log x - \log4 \right) \right] - \frac{1}{2}\left\{ \cos \left( \log\frac{x}{4} \right) + \cos\left( \log4x \right) \right\}\]
\[ = \frac{1}{2}\left\{ \cos (\log 4x) + \cos \left( \log \frac{x}{4} \right) - \cos \left( \log \frac{x}{4} \right) - \cos \left( \log 4x \right) \right\}\]
\[ = \frac{1}{2} \times 0 = 0\]

 

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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 12 | पृष्ठ ४३

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