JEE Main & Advanced Mathematics Definite Integration Question Bank Fundamental definite integration, Definite integration by substitution

  • question_answer
    If \[\int_{\log 2}^{x}{\frac{du}{{{({{e}^{u}}-1)}^{1/2}}}}=\frac{\pi }{6}\], then \[{{e}^{x}}=\]                        [Orissa JEE 2005]

    A) 1

    B) 2

    C) 4             

    D) -1

    Correct Answer: C

    Solution :

               \[\int_{\log 2}^{x}{\frac{du}{{{({{e}^{u}}-1)}^{1/2}}}}=\frac{\pi }{6}\]                    Þ \[\int_{1}^{\sqrt{{{e}^{x}}-1}}{\frac{2t}{1+{{t}^{2}}}}\ dt=\frac{\pi }{6}\]as \[{{e}^{u}}-1={{t}^{2}}\]                    Þ \[2({{\tan }^{-1}}t)_{1}^{\sqrt{{{e}^{x}}-1}}=\frac{\pi }{6}\] Þ \[{{\tan }^{-1}}\sqrt{{{e}^{x}}-1}-\frac{\pi }{4}=\frac{\pi }{12}\]                                 Þ \[\sqrt{{{e}^{x}}-1}=\tan \frac{\pi }{3}\] Þ \[\sqrt{{{e}^{x}}-1}=\sqrt{3}\] Þ \[{{e}^{x}}=4\].


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