JEE Main & Advanced JEE Main Paper (Held On 15 April 2018) Slot-II

  • question_answer
    \[\int_{{}}^{{}}{\frac{2x+5}{\sqrt{7-6x-{{x}^{2}}}}dx=A\sqrt{7-6x-{{x}^{2}}}+B{{\sin }^{-1}}\left( \frac{x+3}{4} \right)+C}\] (where \[C\] is a constant of integration), then the ordered pair \[(A,B)\] is equal to [JEE Online 15-04-2018 (II)]

    A)         \[(-2,-1)\]                           

    B) \[(2,-1)\]             

    C) \[(-2,1)\]             

    D)          \[(2,1)\]

    Correct Answer: A

    Solution :

    Note that \[7-6x-{{x}^{2}}=16-{{(x+3)}^{2}}\] and\[\frac{d}{dx}(7-6x-{{x}^{2}})=-2x-6\] So, we have \[\begin{align}   & \int_{{}}^{{}}{\frac{2x+5}{\sqrt{7-6x-{{x}^{2}}}}dx=\int_{{}}^{{}}{\frac{2x+6}{\sqrt{7-6x-{{x}^{2}}}}dx}} \\  & -\int_{{}}^{{}}{\frac{1}{\sqrt{16-{{(x+3)}^{2}}}}dx} \\ \end{align}\] \[=-2\sqrt{7-6x-{{x}^{2}}}-{{\sin }^{-1}}(\frac{x+3}{4})+C\] So, we have \[A=-2,B=-1\]. Thus option A is the correct answer.


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