JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Integration of Rational Function by Using Partial Fractions

  • question_answer
    \[\int_{{}}^{{}}{\frac{3\sin x+2\cos x}{3\cos x+2\sin x}\ dx=}\]

    A)                 \[\frac{12}{13}x-\frac{5}{13}\log (3\cos x+2\sin x)\]

    B)                 \[\frac{12}{13}x+\frac{5}{13}\log (3\cos x+2\sin x)\]

    C)                 \[\frac{13}{12}x+\frac{5}{13}\log (3\cos x+2\sin x)\]

    D)                 None of these

    Correct Answer: A

    Solution :

                       Write \[{{N}^{r}}=l({{D}^{r}})+m\] (differential coefficient of \[{{D}^{r}}).\]                    Let 3sinx+2cosx = l(3cosx+2sinx)+m(?3sinx + 2cosx)                    Comparing coefficients of \[\sin x\] and \[\cos x\]on both sides \[3=2l-3m\] and \[2=3l+2m\]                    Solving, we get \[l=\frac{12}{13},\] \[m=-\frac{5}{13},\]                    \[\therefore \,\,I=l\,\int_{{}}^{{}}{dx}+m\int_{{}}^{{}}{\frac{-3\sin x+2\cos x}{3\cos x+2\sin x}\,dx}\]                 =lx+mlog(3cosx+2sinx)\[=\frac{12}{13}x-\frac{5}{13}\]log(3cosx+2sinx).


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