J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer
    If \[y=\log \,(\sin \,({{x}^{2}})),\] \[0<0<\frac{\pi }{2},\] then \[\frac{dy}{dx}\] at\[x=\frac{\sqrt{\pi }}{2}\]is

    A)  \[0\]

    B)  \[1\]

    C)  \[\frac{\pi }{4}\]

    D)  \[\sqrt{\pi }\]

    Correct Answer: D

    Solution :

    Given,  \[y=\log \,(\sin \,({{x}^{2}}))\] \[\frac{dy}{dx}=\frac{1}{\sin \,{{x}^{2}}}.\,\cos \,{{x}^{2}}.2x\] \[=2x\,cot\,{{x}^{2}}\] At \[x=\frac{\sqrt{\pi }}{2},\frac{dy}{dx}=\frac{2\sqrt{\pi }}{2}\,\cot \,{{\left( \frac{\sqrt{\pi }}{2} \right)}^{2}}\] \[=\sqrt{\pi }\,\,\cot \,\,\left( \frac{\pi }{4} \right)=\sqrt{\pi }\]


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