CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2002

  • question_answer
    \[\int_{0}^{\frac{\pi }{2}}{\sin 2x}\log \tan x\,dx\]is equal to:

    A)  \[\pi \]                                                

    B)         \[\frac{\pi }{2}\]

    C)         1                                            

    D)         \[2\pi \]

    E)         0

    Correct Answer: E

    Solution :

    Let \[I=\int_{0}^{\pi /2}{\sin 2x\log \tan x\,dx}\]                       ...(i) \[\therefore \]\[I=\int_{0}^{\pi /2}{\sin (\pi -2x)\log \tan \left( \frac{\pi }{2}-x \right)}dx\] \[I=\int_{0}^{\pi /2}{\sin 2x\log \cot x\,\,}dx\]          ...(ii) From Eqs. (i) and (ii), we get \[2I=\int_{0}^{\pi /2}{\sin 2x\log \tan x\,\cot x\,}dx\] \[=\int_{0}^{\pi /2}{\sin 2x\log 1}dx\] \[=0\] \[\Rightarrow \]               \[I=0\] 


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