JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Increasing and Decreasing Function

  • question_answer
    The length of the longest interval, in which the function \[3\sin x-4\sin x\] is increasing, is                            [IIT Screening 2002]

    A)            \[\frac{\pi }{3}\]

    B)            \[\frac{\pi }{2}\]

    C)            \[\frac{3\pi }{2}\]

    D)            \[\pi \]

    Correct Answer: A

    Solution :

               \[3\sin x-4{{\sin }^{3}}x=\sin 3x\]            It is increasing, when \[-\pi /2\le 3x\le \pi /2\]            i.e.,\[-\pi /6\le x\le \pi /6\].            The length of interval = \[\left| \,\frac{\pi }{6}-\left( -\frac{\pi }{6} \right)\, \right|\,=\,\frac{\pi }{3}\].


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