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If F ( X ) = X + 1 X − 1 , Show that F[F[(X)]] = X. - Mathematics

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Question

If  \[f\left( x \right) = \frac{x + 1}{x - 1}\] , show that f[f[(x)]] = x.

 

 

Solution

Given:

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

Therefore,

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

\[= \frac{\left( \frac{x + 1}{x - 1} \right) + 1}{\left( \frac{x + 1}{x - 1} \right) - 1}\]
\[= \frac{\frac{x + 1 + x - 1}{x - 1}}{\frac{x + 1 - x + 1}{x - 1}} = \frac{\frac{2x}{x - 1}}{\frac{2}{x - 1}} = \frac{2x}{2} = x\]
Thus,
f {(x)}] = x
Hence proved.
 
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Chapter 3: Functions - Exercise 3.2 [Page 11]

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RD Sharma Mathematics [English] Class 11
Chapter 3 Functions
Exercise 3.2 | Q 5 | Page 11

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