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

  • question_answer
    \[\int_{\,2}^{\,3}{\frac{dx}{{{x}^{2}}-x}=}\]                                         [EAMCET 2002]

    A)                 \[\log (2/3)\]     

    B)                 \[\log (1/4)\]

    C)                 \[\log (4/3)\]     

    D)                 \[\log (8/3)\]

    Correct Answer: C

    Solution :

               \[I=\int_{2}^{3}{\frac{dx}{{{x}^{2}}-x}}\]\[=\int_{2}^{3}{\frac{dx}{x\,(x-1)}}\]\[=\int_{2}^{3}{\left[ \frac{1}{x-1}-\frac{1}{x} \right]}\,dx\]              \[=\int_{2}^{3}{\frac{1}{(x-1)}}\,dx-\int_{2}^{3}{\frac{1}{x}dx}\]\[=[\log (x-1)]_{2}^{3}-[\log x]_{2}^{3}\]       \[=[\log 2-\log 1]-[\log 3-\log 2]\]\[=2\log 2-\log 3=\log \frac{4}{3}\].


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