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

  • question_answer
    Let \[{{I}_{1}}=\int_{1}^{2}{\frac{dx}{\sqrt{1+{{x}^{2}}}}}\]and\[{{I}_{2}}=\int_{1}^{2}{\frac{dx}{x}}\] then          [Pb. CET 2004]

    A)                 \[{{I}_{1}}>{{I}_{2}}\]    

    B)                 \[{{I}_{2}}>{{I}_{1}}\]

    C)                 \[{{I}_{1}}={{I}_{2}}\]    

    D)                 \[{{I}_{1}}>2{{I}_{2}}\]

    Correct Answer: B

    Solution :

               We have, \[(1+{{x}^{2}})>{{x}^{2}},\forall x\]; \[\sqrt{1+{{x}^{2}}}>x,\forall \,x\in (1,\,2)\]                    Þ \[\frac{1}{\sqrt{1+{{x}^{2}}}}<\frac{1}{x},\,\,\forall x\in (1,\,2)\]Þ \[\int_{1}^{2}{\frac{dx}{\sqrt{1+{{x}^{2}}}}<\int_{1}^{\,2}{\frac{dx}{x}}}\]                                 Þ  \[{{I}_{1}}<{{I}_{2}}\]Þ \[{{I}_{2}}>{{I}_{1}}\].


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