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

  • question_answer
    The solution of the differential equation \[\frac{dy}{dx}+y=\cos x\]is [AISSE 1990]

    A)                 \[y=\frac{1}{2}(\cos x+\sin x)+c{{e}^{-x}}\]              

    B)                 \[y=\frac{1}{2}(\cos x-\sin x)+c{{e}^{-x}}\]

    C)                 \[y=\cos x+\sin x+c{{e}^{-x}}\]     

    D)                 None of these

    Correct Answer: A

    Solution :

                       It is linear equation of the form \[\frac{dy}{dx}+Py=Q\]         So, I.F. \[={{e}^{\int_{{}}^{{}}{1dx}}}={{e}^{x}}\]         Hence solution is \[y.{{e}^{x}}=\int_{{}}^{{}}{\cos x.{{e}^{x}}dx+c}\]                 Þ \[y=\frac{1}{2}(\cos x+\sin x)+c{{e}^{-x}}\].


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