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If F ( X ) = X − 1 X + 1 , Then Show that (I) F ( 1 X ) = − F ( X ) (Ii) F ( − 1 X ) = − 1 F ( X ) - Mathematics

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Question

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

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

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

Solution

Given:

\[f\left( x \right) = \frac{x - 1}{x + 1}\]       .....(1) 
(i) Replacing  by
 
\[\frac{1}{x}\]  in (1), we get
 

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

\[ = \frac{1 - x}{1 + x}\]

\[ = - \frac{x - 1}{x + 1}\]

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

(ii) Replacing  by

\[- \frac{1}{x}\]  in (1), we get

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

\[ = \frac{- 1 - x}{- 1 + x}\]

\[ = - \frac{x + 1}{x - 1}\]

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

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

 
 
 
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Chapter 3: Functions - Exercise 3.2 [Page 12]

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RD Sharma Mathematics [English] Class 11
Chapter 3 Functions
Exercise 3.2 | Q 9 | Page 12

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