JEE Main & Advanced Mathematics Definite Integration Question Bank Fundamental definite integration, Definite integration by substitution

  • question_answer
    \[\int_{0}^{\pi /2}{{{e}^{x}}\sin x\,dx=}\]                                              [Roorkee 1978]

    A)                 \[\frac{1}{2}({{e}^{\pi /2}}-1)\]

    B)                 \[\frac{1}{2}({{e}^{\pi /2}}+1)\]

    C)                 \[\frac{1}{2}(1-{{e}^{\pi /2}})\]

    D)                 \[2({{e}^{\pi /2}}+1)\]

    Correct Answer: B

    Solution :

                Let \[I=\int_{0}^{\pi /2}{{{e}^{x}}\sin \,x\,\,dx}\]                             = \[-[{{e}^{x}}\cos x]_{0}^{\pi /2}+\int_{0}^{\pi /2}{{{e}^{x}}\cos x\,dx}\]                             \[=-[{{e}^{x}}\cos x]_{0}^{\pi /2}+[{{e}^{x}}\sin x]_{0}^{\pi /2}-\int_{0}^{\pi /2}{{{e}^{x}}\sin x\,dx}\]                    \[\therefore \]\[2I=[{{e}^{x}}(\sin x-\cos x)]_{0}^{\pi /2}=({{e}^{\pi /2}}+1)\]                                 Hence \[\int_{0}^{\pi /2}{{{e}^{x}}\sin xdx=\frac{1}{2}({{e}^{\pi /2}}+1)}\].


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