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

  • question_answer
    \[\int_{0}^{1}{{{\tan }^{-1}}x\,dx=}\]     [Karnataka CET 1993; RPET 1997]

    A)                 \[\frac{\pi }{4}-\frac{1}{2}\log 2\]            

    B)                 \[\pi -\frac{1}{2}\log 2\]

    C)                 \[\frac{\pi }{4}-\log 2\] 

    D)                 \[\pi -\log 2\]

    Correct Answer: A

    Solution :

               Put \[x=\tan \theta \Rightarrow dx={{\sec }^{2}}\theta \,\,d\theta \]            Also as \[x=0,\theta =0\]and \[x=1,\theta =\frac{\pi }{4}\]            Therefore, \[\int_{0}^{1}{{{\tan }^{-1}}x\,dx=\int_{0}^{\pi /4}{\theta {{\sec }^{2}}\theta \,d\theta }}\]                                                            \[=\frac{\pi }{4}\]\[-\log \sqrt{2}=\frac{\pi }{4}-\frac{1}{2}\log 2\].


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