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

  • question_answer
    A value of \[\alpha \]such that \[\int\limits_{\alpha }^{\alpha +1}{\frac{dx}{\left( x+\alpha  \right)\left( x+\alpha +1 \right)}}={{\log }_{e}}\left( \frac{9}{8} \right)\]is: [JEE Main 12-4-2019 Afternoon]

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

    B) \[2\]

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

    D) \[-2\]

    Correct Answer: D

    Solution :

    \[\int\limits_{\alpha }^{\alpha +1}{\frac{\left( x+\alpha +1 \right)-\left( x+\alpha  \right)}{\left( x+\alpha  \right)\left( x+\alpha +1 \right)}dx}=\]           \[\left( \ell n\left| x+\alpha  \right|-\ell n\left| x+\alpha +1 \right| \right)_{\alpha }^{\alpha +1}\]           \[=\ell n\left| \frac{2\alpha +1}{2\alpha +2}\times \frac{2\alpha +1}{2\alpha } \right|=\ell n\frac{9}{8}\]\[\Rightarrow \alpha =-2,1\]


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