JEE Main & Advanced Mathematics Definite Integration Question Bank Fundamental definite integration, Definite integration by substitution

  • question_answer
    \[\int_{\,1}^{\,x}{\frac{\log {{x}^{2}}}{x}\,dx=}\]                                               [DCE 1999]

    A)                 \[{{(\log x)}^{2}}\]          

    B)                 \[\frac{1}{2}{{(\log x)}^{2}}\]

    C)                 \[\frac{\log {{x}^{2}}}{2}\]           

    D)                 None of these

    Correct Answer: A

    Solution :

               \[I=\int_{1}^{x}{\frac{2\log x}{x}dx}\]            Let \[\log x=t\] Þ \[\frac{dx}{x}=dt\]                                 \[\therefore I=2\int_{0}^{\log x}{t\,dt=2\,\left[ \frac{{{t}^{2}}}{2} \right]}_{0}^{\log x}={{(\log x)}^{2}}\].


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