JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Fundamental Integration

  • question_answer
    \[\int_{{}}^{{}}{\frac{\sin x}{\sin (x-\alpha )}dx=}\] [RPET 1999; Kerala (Engg.) 2002; AIEEE 2004]

    A)            \[x\cos \alpha -\sin \alpha \log \sin (x-\alpha )+c\]

    B)            \[x\cos \alpha +\sin \alpha \log \sin (x-\alpha )+c\]

    C)            \[x\sin \alpha -\sin \alpha \log \sin (x-\alpha )+c\]

    D)            None of these

    Correct Answer: B

    Solution :

               \[\int_{{}}^{{}}{\frac{\sin x}{\sin (x-\alpha )}\,dx=\int_{{}}^{{}}{\frac{\sin (x-\alpha +\alpha )}{\sin (x-\alpha )}\,dx}}\]                    \[=\int_{{}}^{{}}{\frac{\left\{ (\sin (x-\alpha )\cos \alpha +\cos (x-\alpha )\sin \alpha  \right\}}{\sin (x-\alpha )}\,dx}\]                    \[=\int_{{}}^{{}}{\cos \alpha \,dx+\int_{{}}^{{}}{\sin \alpha \,.\,\cot \,(x-\alpha )\,dx}}\]                    \[=x\cos \alpha +\sin \alpha \,.\,\log \sin (x-\alpha )+c\].


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