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

  • question_answer
    \[\int_{{}}^{{}}{\frac{\sin x}{\sin x-\cos x}}\ dx=\]           [Roorkee 1988]

    A)            \[\frac{1}{2}\log (\sin x-\cos x)+x+c\]                           

    B)            \[\frac{1}{2}[\log (\sin x-\cos x)+x]+c\]

    C)            \[\frac{1}{2}\log (\cos x-\sin x)+x+c\]                           

    D)            \[\frac{1}{2}[\log (\cos x-\sin x)+x]+c\]

    Correct Answer: B

    Solution :

                       \[\int_{{}}^{{}}{\frac{\sin x\,dx}{\sin x-\cos x}}=\frac{1}{2}\int_{{}}^{{}}{\frac{2\sin x}{\sin x-\cos x}\,dx}\]            \[=\frac{1}{2}\int_{{}}^{{}}{\frac{(\sin x-\cos x+\sin x+\cos x)}{\sin x-\cos x}\,dx}\]                    \[=\frac{1}{2}\int_{{}}^{{}}{\left( 1+\frac{\sin x+\cos x}{\sin x-\cos x} \right)\,dx}=\frac{1}{2}[x+\log (\sin x-\cos x)]+c\].


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