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

  • question_answer
    The value of \[\int_{1}^{{{e}^{2}}}{\frac{dx}{x{{(1+\ln x)}^{2}}}}\] is                        [J & K 2005]

    A)                 \[2/3\] 

    B)                 \[1/3\]

    C)                 \[3/2\] 

    D)                 \[\ln 2\]

    Correct Answer: A

    Solution :

               \[I=\int_{1}^{{{e}^{2}}}{\frac{dx}{x{{(1+\ln x)}^{2}}}}\]            Let \[(1+\ln x)=t\] Þ  \[dt=\frac{1}{x}dx\]            Now, when \[x=1\to {{e}^{2}}\], then \[t=1\to 3\]                 \[\therefore \] \[I=\int_{1}^{3}{\frac{dt}{{{t}^{2}}}=\left[ \frac{-1}{t} \right]_{1}^{3}=-\left[ \frac{1}{3}-1 \right]}=\frac{2}{3}\].


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