JEE Main & Advanced JEE Main Paper (Held on 12-4-2019 Morning)

  • question_answer
    If\[\int\limits_{0}^{\frac{\pi }{2}}{\frac{\cot x}{\cot x+\cos ecx}}dx=m(\pi +n),\]then m. n is equal to: [JEE Main Held on 12-4-2019 Morning]

    A) \[-1\]   

    B) \[1\]

    C) \[\frac{1}{2}\]                        

    D) \[-\frac{1}{2}\]

    Correct Answer: A

    Solution :

    \[\int\limits_{0}^{\pi /2}{\frac{\cot \,xdx}{\cot \,x+cosecx}}\] \[\int\limits_{0}^{\pi /2}{\frac{\cot \,x}{cos\,x+1}=\int_{{}}^{{}}{\frac{2{{\cos }^{2}}\frac{x}{2}-1}{2{{\cos }^{2}}\frac{x}{2}}}}\] \[\int\limits_{0}^{\pi /2}{\left( 1-\frac{1}{2}{{\sec }^{2}}\frac{\,x}{2} \right)dx}\]\[\left[ x-\tan \frac{x}{2} \right]_{0}^{\frac{\pi }{2}}\] \[\frac{1}{2}[\pi -2]\]  \[m=\frac{1}{2},n=-2\]         \[mn=-1\]                   


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