J & K CET Engineering J and K - CET Engineering Solved Paper-2003

  • question_answer
    \[\int_{0}^{1}{\log \,\left\{ \sin \left( \frac{\pi \,\,x}{2} \right) \right\}}\,\,dx\] is equal to

    A)  \[-\frac{\pi }{2}\log \,2\]

    B)  \[-\,\log \,\,\,2\]

    C)  \[-\frac{\pi }{2}\,\log \,2\]

    D)  \[\frac{\pi }{2}\,\log \,2\]

    Correct Answer: B

    Solution :

    Let \[I=\int_{0}^{1}{\log \left\{ \sin \,\left( \frac{\pi \,x}{2} \right) \right\}}dx\] Put  \[\frac{\pi \,x}{2}=\theta \Rightarrow \,dx=\frac{2}{\pi }d\theta \] \[\therefore \] \[I=\frac{2}{\pi }\int_{0}^{\pi /2}{\log \,\,\sin \theta \,d\theta }\] \[=\frac{2}{\pi }\left( -\frac{\pi }{2}\,\log \,2 \right)\] \[=-\log \,2\]


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