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

  • question_answer
    If \[\int_{{}}^{{}}{{{e}^{x}}\sin x\ dx=\frac{1}{2}{{e}^{x}}\ .\ a+c}\], then \[a=\] [MP PET 1989]

    A)                 \[\sin x-\cos x\]

    B)                 \[\cos x-\sin x\]

    C)                 \[-\cos x-\sin x\]

    D)                 \[\cos x+\sin x\]

    Correct Answer: A

    Solution :

                    Given that \[\int_{{}}^{{}}{{{e}^{x}}\sin x\,dx}=\frac{1}{2}{{e}^{x}}a+c\]                ..?(i)                 Let \[I=\int_{{}}^{{}}{{{e}^{x}}\sin x\,dx}=-{{e}^{x}}\cos x+\int_{{}}^{{}}{{{e}^{x}}\cos x\,dx+c}\]                         \[=-{{e}^{x}}\cos x+{{e}^{x}}\sin x-\int_{{}}^{{}}{{{e}^{x}}\sin x\,dx+c}\]                 \[\Rightarrow 2I={{e}^{x}}(-\cos x+\sin x)+c\]. Now from (i), we get                 \[\frac{1}{2}{{e}^{x}}a=\frac{1}{2}{{e}^{x}}(\sin x-\cos x)\Rightarrow a=\sin x-\cos x.\]


You need to login to perform this action.
You will be redirected in 3 sec spinner