KVPY Sample Paper KVPY Stream-SX Model Paper-29

  • question_answer
    If\[\int_{{}}^{{}}{{{x}^{5}}{{e}^{-4{{x}^{3}}}}dx=\frac{1}{48}{{e}^{-4{{x}^{3}}}}}f(x)+C,\] where C is a constant of integration, then\[f(x)\] is equal to:

    A) \[-2{{x}^{3}}-1\]

    B) \[-4{{x}^{3}}-1\]

    C) \[-2{{x}^{3}}+1\]

    D) \[4{{x}^{3}}+1\]

    Correct Answer: B

    Solution :

    \[\int{{{x}^{5}}.{{e}^{-4{{x}^{3}}}}dx}\]
    \[=\int{{{x}^{2}}.{{x}^{3}}{{e}^{-4{{x}^{3}}}}dx}\]
    \[-4{{x}^{3}}=t\]
    \[-12{{x}^{2}}dx=dt\]
    \[=\frac{-1}{12}\int{-\frac{t}{4}{{e}^{t}}dt}\]
    \[=\frac{1}{48}\int{t{{e}^{t}}dt}\]
    \[=\frac{1}{48}t{{e}^{t}}-1.{{e}^{t}}+c\]
    \[=\frac{1}{48}{{e}^{-4{{x}^{3}}}}..(-4{{x}^{3}})-{{e}^{-4{{x}^{3}}}}+c.\]


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