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

  • question_answer
    \[\int_{{}}^{{}}{{{x}^{3}}\sqrt{3+5{{x}^{4}}}}\ dx=\]            [DSSE 1982]

    A)            \[{{(3+5{{x}^{4}})}^{3/2}}+c\]

    B)            \[\frac{1}{5}{{(3+5{{x}^{4}})}^{3/2}}+c\]

    C)            \[\frac{1}{30}{{(3+5{{x}^{4}})}^{3/2}}+c\]

    D)            None of these

    Correct Answer: C

    Solution :

                       Put \[3+5{{x}^{4}}=t\Rightarrow 20{{x}^{3}}dx=dt,\] then            \[\int_{{}}^{{}}{{{x}^{3}}\sqrt{3+5{{x}^{4}}}dx}=\frac{1}{20}\int_{{}}^{{}}{{{t}^{1/2}}dt}\]                    \[=\frac{2}{3}\times \frac{1}{20}.{{t}^{3/2}}+c=\frac{1}{30}{{(3+5{{x}^{4}})}^{3/2}}+c.\]


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