JEE Main & Advanced JEE Main Solved Paper-2015

  • question_answer
    The integral \[\int\limits_{2}^{4}{\frac{\log {{x}^{2}}}{\log {{x}^{2}}+\log \left( 36-12x+{{x}^{2}} \right)}dx}\] is equal to : [JEE Main Solved Paper-2015 ]

    A) 1                                             

    B) 6

    C) 2                                             

    D) 4

    Correct Answer: A

    Solution :

    \[I=\int\limits_{2}^{4}{\frac{\log {{x}^{2}}}{\log {{x}^{2}}+\log \left( 6-x \right)}dx}\]                       ?.(1) Using property \[\int\limits_{a}^{b}{f\left( a+b-x \right)dx}=\int\limits_{a}^{b}{f\left( x \right)dx}\] \[I=\int\limits_{2}^{b}{\frac{\log {{\left( 6-x \right)}^{2}}}{\log {{\left( 6-x \right)}^{2}}+\log {{x}^{2}}}dx}\]                                ?(2) (1)+ (2) \[\Rightarrow \] \[I=\frac{1}{2}\int\limits_{2}^{4}{\frac{\cancel{\log {{x}^{2}}+\log {{\left( 6-x \right)}^{2}}}}{\cancel{\log {{x}^{2}}+\log {{\left( 6-x \right)}^{2}}}}}dx\] \[I=\frac{1}{2}\int\limits_{2}^{4}{dx}=\frac{1}{2}\left[ 4-2 \right]=1\]


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