JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Integration by Substitution

  • question_answer
    \[\int_{{}}^{{}}{\tan x}{{\sec }^{2}}x\sqrt{1-{{\tan }^{2}}x}\ dx=\]

    A)            \[-\frac{1}{3}{{(1-{{\tan }^{2}}x)}^{3/2}}+c\]

    B)            \[\frac{1}{3}{{(1-{{\tan }^{2}}x)}^{3/2}}+c\]

    C)            \[-\frac{2}{3}{{(1-{{\tan }^{2}}x)}^{2/3}}+c\]

    D)            None of these

    Correct Answer: A

    Solution :

                       \[\int_{{}}^{{}}{\tan x\,.\,{{\sec }^{2}}x\sqrt{1-{{\tan }^{2}}x}\,dx}\] Put \[\tan x=t\Rightarrow {{\sec }^{2}}x\,dx=dt,\] then it reduces to \[\int_{{}}^{{}}{t\sqrt{1-{{t}^{2}}}\,dt}\]            Now again, put \[1-{{t}^{2}}=u,\] then its reduced form is            \[-\frac{1}{2}\int_{{}}^{{}}{\sqrt{u}\,du}=-\frac{1}{3}{{u}^{3/2}}+c=-\frac{1}{3}{{(1-{{\tan }^{2}}x)}^{3/2}}+c.\]


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