JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Self Evaluation Test - Integrals

  • question_answer
    The tangent of the curve \[y=f(x)\] at the point with abscissa \[x=1\] from an angle of \[\pi /6\] and at the point \[x=2\] an angle of \[\pi /3\] and at the point \[x=3\] an angle of \[\pi /4\]. If \[f''(x)\] is continuous, then the value of \[\int\limits_{1}^{3}{f''(x)f'(x)dx+\int\limits_{2}^{3}{f''(x)dx}}\] is

    A) \[\frac{4\sqrt{3}-1}{3\sqrt{3}}\]

    B) \[\frac{3\sqrt{3}-1}{2}\]

    C) \[\frac{4-3\sqrt{3}}{3}\]

    D) None of these

    Correct Answer: C

    Solution :

    [c] According to question \[f'(1)=tan\frac{\pi }{6}=\frac{1}{\sqrt{3}}\] \[f'(2)=tan\frac{\pi }{3}=\sqrt{3}\] and \[f'(3)=tan\frac{\pi }{4}=1\] so, \[\int\limits_{1}^{3}{f''(x)f'(x)dx+\int\limits_{1}^{3}{f''(x)dx}}\] \[=\left[ \frac{{{\left\{ f'(x) \right\}}^{2}}}{2} \right]_{1}^{3}+\left[ f'(x) \right]_{2}^{3}\] \[=\frac{1}{2}\left[ 1-\frac{1}{3} \right]+\left[ 1-\sqrt{3} \right]=\frac{4}{3}-\sqrt{3}\]


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