JEE Main & Advanced Mathematics Differential Equations Question Bank Linear defferential equations

  • question_answer
    An integrating factor for the differential equation \[(1+{{y}^{2}})dx-({{\tan }^{-1}}y-x)dy=0\]         [MP PET 1993]

    A)                 \[{{\tan }^{-1}}y\]             

    B)                 \[{{e}^{{{\tan }^{-1}}y}}\]

    C)                 \[\frac{1}{1+{{y}^{2}}}\]               

    D)                 \[\frac{1}{x(1+{{y}^{2}})}\]

    Correct Answer: B

    Solution :

                       \[(1+{{y}^{2}})dx-({{\tan }^{-1}}y-x)dy=0\]                    Þ \[\frac{dy}{dx}=\frac{1+{{y}^{2}}}{{{\tan }^{-1}}y-x}\] Þ \[\frac{dx}{dy}=\frac{{{\tan }^{-1}}y}{1+{{y}^{2}}}-\frac{x}{1+{{y}^{2}}}\]                    Þ \[\frac{dx}{dy}+\frac{x}{1+{{y}^{2}}}=\frac{{{\tan }^{-1}}y}{1+{{y}^{2}}}\]                    This is equation of the form \[\frac{dx}{dy}+Px=Q\]                                 So, I.F. \[={{e}^{\int{P\,dy}}}={{e}^{\int{\frac{1}{1+{{y}^{2}}}.dy}}}={{e}^{{{\tan }^{-1}}y}}\].


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