JEE Main & Advanced Sample Paper JEE Main Sample Paper-20

  • question_answer
    The value of the definite integral,\[\int\limits_{{{\theta }_{1}}}^{{{\theta }_{2}}}{\frac{d\theta }{1+\tan \theta }}=\frac{501\pi }{K}\]where\[{{\theta }_{2}}=\frac{1003\pi }{2008}\]and\[{{\theta }_{1}}=\frac{\pi }{2008}\]. The value of \[K\] equals

    A) \[2007\]                              

    B) \[2006\]

    C) \[2009\]                              

    D) \[2008\]

    Correct Answer: D

    Solution :

    \[{{\theta }_{1}}+{{\theta }_{2}}=\frac{\pi }{2}\] \[\therefore \]  \[I=\int\limits_{{{\theta }_{1}}}^{{{\theta }_{2}}}{\frac{d\theta }{1+\tan \left( \frac{\pi }{2}-\theta  \right)}=\int\limits_{{{\theta }_{1}}}^{{{\theta }_{2}}}{\frac{\tan \theta \,\,d\theta }{1+\tan \theta }}}\] and also\[I=\int_{{{\theta }_{1}}}^{{{\theta }_{2}}}{\frac{d\theta }{1+\tan \theta }}\] \[\therefore \]\[2I=\int\limits_{{{\theta }_{1}}}^{{{\theta }_{2}}}{d\theta ={{\theta }_{2}}-{{\theta }_{1}}}=\frac{1002\pi }{2008}\Rightarrow I=\frac{501\pi }{2008}\] Hence\[,\]\[K=2008\].


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