JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Self Evaluation Test - Integrals

  • question_answer
    If \[\int{{{\sin }^{3}}x{{\cos }^{5}}xdx}\]\[=A{{\sin }^{4}}x+B{{\sin }^{6}}x+C{{\sin }^{8}}x+D\] Then

    A) \[A=\frac{1}{4},B=-\frac{1}{3},C=\frac{1}{8},D\in R\]

    B) \[A=\frac{1}{8},B=\frac{1}{4},C=\frac{1}{3},D\in R\]

    C) \[A=0,B=-\frac{1}{6},C=\frac{1}{8},D\in R\]

    D) None of these

    Correct Answer: A

    Solution :

    [a] \[I=\int{{{\sin }^{3}}x.{{\cos }^{5}}xdx}\] Put \[\sin \,\,x=t\Rightarrow cos\,\,x\,\,dx=dt\] \[I=\int{{{\sin }^{3}}x.{{\cos }^{4}}x.\cos x\,\,dx=\int{{{t}^{3}}{{\left( 1-{{t}^{2}} \right)}^{2}}dt}}\] \[=\int{\left( {{t}^{3}}-2{{t}^{5}}+{{t}^{7}} \right)dt=\frac{1}{4}{{t}^{4}}-\frac{2}{6}{{t}^{6}}+\frac{1}{8}{{t}^{8}}+D}\] \[=\frac{1}{4}{{\sin }^{4}}x-\frac{1}{3}{{\sin }^{6}}x+\frac{1}{8}{{\sin }^{8}}x+D\]


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