JCECE Engineering JCECE Engineering Solved Paper-2015

  • question_answer
    If\[0\le x<1\], then\[\sin \left\{ {{\tan }^{-1}}\frac{1-{{x}^{2}}}{2x}+{{\cos }^{-1}}\frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right\}\]is equal to

    A) \[1\]

    B) \[-1\]

    C) \[0\]

    D)  None of the above

    Correct Answer: A

    Solution :

    We know that, \[{{\tan }^{-1}}\left( \frac{2x}{1-{{x}^{2}}} \right)=2{{\tan }^{-1}}x,\]if\[-1<x<1\] and\[{{\cos }^{-1}}\left( \frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right)=2{{\tan }^{-1}}x,\]if\[0\le x\le \infty \] \[\therefore \]  \[\sin \left\{ {{\tan }^{-1}}\frac{1-{{x}^{2}}}{2x}+{{\cos }^{-1}}\frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right\}\]                 \[=\sin \left\{ {{\cot }^{-1}}\frac{2x}{1-{{x}^{2}}}+{{\cos }^{-1}}\frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right\}\] \[=\sin \left\{ \frac{\pi }{2}-{{\tan }^{-1}}\frac{2x}{1-{{x}^{2}}}+{{\cos }^{-1}}\frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right\}\]                 \[=\sin \left\{ \frac{\pi }{2}-2{{\tan }^{-1}}x+2{{\tan }^{-1}}x \right\}\], if                 \[0\le x<1\]                 \[=\sin \frac{\pi }{2}=1\]


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