JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2013

  • question_answer
        The smallest and the largest values of\[{{\tan }^{-1}}\left( \frac{1-x}{1+x} \right),\]where\[0\le x\le 1,\]are

    A)  \[0,\pi \]                                            

    B)  \[1\]

    C)  \[5\]                                    

    D)  \[10\]

    Correct Answer: B

    Solution :

                    We have, \[{{\tan }^{-1}}\left( \frac{1-x}{1+x} \right)={{\tan }^{-1}}(1)-{{\tan }^{-1}}x\] \[=\frac{\pi }{4}-{{\tan }^{-1}}x\] Since,     \[0\le x\le 1\] Then,      \[0\le {{\tan }^{-1}}x\le \frac{\pi }{4}\] \[\Rightarrow \]               \[0\ge -{{\tan }^{-1}}x\ge -\frac{\pi }{4}\] \[\Rightarrow \]               \[\frac{\pi }{4}\ge \frac{\pi }{4}-{{\tan }^{-1}}x\ge 0\] \[\Rightarrow \]               \[\frac{\pi }{4}\ge {{\tan }^{-1}}\left\{ \frac{(1-x)}{(1+x)} \right\}\ge 0\]


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