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

  • question_answer
    \[\int_{{}}^{{}}{{{\sin }^{-1}}(3x-4{{x}^{3}})dx=}\]             [AISSE 1986; DSSE 1984]

    A)                 \[x{{\sin }^{-1}}x+\sqrt{1-{{x}^{2}}}+c\]

    B)                 \[x{{\sin }^{-1}}x-\sqrt{1-{{x}^{2}}}+c\]

    C)                 \[2[x{{\sin }^{-1}}x+\sqrt{1-{{x}^{2}}}]+c\]

    D)                 \[3[x{{\sin }^{-1}}x+\sqrt{1-{{x}^{2}}}]+c\]

    Correct Answer: D

    Solution :

                    Put \[x=\sin \theta \Rightarrow dx=\cos \theta \,d\theta ,\] therefore                 \[\int_{{}}^{{}}{{{\sin }^{-1}}(3x-4{{x}^{3}})}\,dx=\int_{{}}^{{}}{{{\sin }^{-1}}(\sin 3\theta )\cos \theta \,d\theta }\]                        \[=\int_{{}}^{{}}{3\theta \cos \theta \,d\theta }=3\left\{ \theta \sin \theta -\int_{{}}^{{}}{\sin \theta \,d\theta } \right\}\]                        \[=3\left\{ \theta \sin \theta +\cos \theta  \right\}+c=3\left\{ x{{\sin }^{-1}}x+\sqrt{1-{{x}^{2}}} \right\}+c.\]


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