JEE Main & Advanced JEE Main Paper (Held On 8 April 2017)

  • question_answer
    The integral\[\int\limits_{\frac{\pi }{12}}^{\frac{\pi }{4}}{\frac{8\cos 2x}{{{(tanx+cosx)}^{3}}}}dx\]equals: [JEE Online 08-04-2017]

    A) \[\frac{13}{256}\]                                            

    B) \[\frac{15}{64}\]

    C) \[\frac{13}{32}\]                                              

    D) \[\frac{15}{128}\]

    Correct Answer: D

    Solution :

    \[\int\limits_{\frac{\pi }{12}}^{\frac{\pi }{4}}{\frac{\cos 2x}{{{\left( \frac{1}{\sin 2x} \right)}^{3}}}}=\int\limits_{\frac{\pi }{12}}^{\frac{\pi }{4}}{\cos 2x\times \sin 2x.{{\sin }^{2}}(2x)dx}\]                \[=\frac{1}{4}\int_{{}}^{{}}{\sin 4x.(1-cos4x)dx}\]                 \[=\frac{1}{4}\int\limits_{\frac{\pi }{12}}^{\frac{\pi }{4}}{\sin 4x}-\int\limits_{\frac{\pi }{12}}^{\frac{\pi }{4}}{\sin 8x}\]


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