RAJASTHAN ­ PET Rajasthan PET Solved Paper-2002

  • question_answer
    \[\int_{0}^{\pi /2}{\log \tan xdx}\]is equal to

    A)  \[0\]

    B)  \[\pi \]

    C)  \[\frac{\pi }{2}\]

    D)  \[\frac{\pi }{4}\]

    Correct Answer: A

    Solution :

     Let \[I=\int_{0}^{\pi /2}{\log \tan xdx}\]   ...(i) \[I=\int_{0}^{\pi /2}{\log \tan \left( \frac{\pi }{2}-x \right)}dx\] \[\Rightarrow \] \[I=\int_{0}^{\pi /2}{\log \cot x}dx\] ?.(ii) On adding Eqs. (i) and (ii), \[2I=\int_{0}^{\pi /2}{\log (\tan x.\cot x)}dx\] \[=\int_{0}^{\pi /2}{\log (1)}dx\] \[\Rightarrow \] \[2I=0\] \[\Rightarrow \] \[I=0\]


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