KVPY Sample Paper KVPY Stream-SX Model Paper-31

  • question_answer
    Let \[2y{{\left( {{\cot }^{-1}}\left( \frac{\sqrt{3}\cos x-\sin x}{\cos x+\sqrt{3}\sin x} \right) \right)}^{2}},\] then \[\frac{dy}{dx}\] is equal to:

    A) \[x-\frac{\pi }{6}\]

    B) \[x+\frac{\pi }{6}\]

    C) \[2x-\frac{\pi }{6}\]

    D) \[2x-\frac{\pi }{3}\]

    Correct Answer: A

    Solution :

    \[2y={{\left( {{\cot }^{-1}}\left( \frac{\sqrt{3}\cos x+\sin x}{\cos x-\sqrt{3}\sin x} \right) \right)}^{2}}\]
    \[2y={{\left( {{\cot }^{-1}}\left( \frac{\sqrt{3}+\tan x}{1-\sqrt{3}\tan x} \right) \right)}^{2}}\]
    \[2y={{\left( {{\cot }^{-1}}\left( \tan \left( \frac{\pi }{3}+x \right) \right) \right)}^{2}}\]
    \[2y={{\left( \frac{\pi }{2}-{{\tan }^{-1}}\left( \tan \left( \frac{\pi }{2}+x \right) \right) \right)}^{2}}\]
    \[={{\left( \frac{\pi }{2}-\left( \frac{\pi }{3}+x \right) \right)}^{2}}\]
    \[2y={{\left( x-\frac{\pi }{6} \right)}^{2}}\]
    \[2y={{x}^{2}}-\frac{\pi }{3}+\frac{{{\pi }^{2}}}{36}\]
    \[y'=x-\frac{\pi }{6}.\]


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