CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2011

  • question_answer
    If\[y={{\sin }^{2}}{{\cot }^{-1}}\sqrt{\frac{1+x}{1-x}},\]then\[\frac{dy}{dx}\]is equal to

    A)  \[2\sin 2x\]                       

    B)  \[\sin 2x\]         

    C)         \[\frac{1}{2}\]                  

    D)         \[-\frac{1}{2}\]

    E)  \[\cos 2x\]

    Correct Answer: D

    Solution :

    \[y={{\sin }^{2}}{{\cot }^{-1}}\sqrt{\frac{1+x}{1-x}}\] Put,        \[x=\cos \theta \] \[\Rightarrow \]               \[\theta ={{\cos }^{-1}}x\]                              ...(i) \[y={{\sin }^{2}}{{\cot }^{-1}}\sqrt{\frac{1+\cos \theta }{1-\cos \theta }}\] \[y={{\sin }^{2}}{{\cot }^{-1}}\sqrt{\frac{2{{\cos }^{2}}\theta /2}{2{{\sin }^{2}}\theta /2}}\] \[y={{\sin }^{2}}{{\cot }^{-1}}(\cot \theta /2)\] \[y={{\sin }^{2}}\theta /2\] \[y=\frac{1-\cos \theta }{2}\] \[y=\frac{1-x}{2}\]                   [From Eq.(i)] Differentiating w.r.t.\[x,\]we get                 \[\frac{dy}{dx}=-\frac{1}{2}\]


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