BCECE Engineering BCECE Engineering Solved Paper-2004

  • question_answer
    \[\int_{1}^{x}{\frac{\log ({{x}^{2}})}{x}}dx\]is equal to:

    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 :

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


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