JEE Main & Advanced Mathematics Differential Equations Question Bank Variable Separable type differential equations

  • question_answer
    Solution of \[\frac{dy}{dx}=\frac{x\log {{x}^{2}}+x}{\sin y+y\,\,\cos y}\] is           [EAMCET 2003]

    A)                 \[y\sin y={{x}^{2}}\log x+c\]         

    B)                 \[y\sin y={{x}^{2}}+c\]

    C)                 \[y\sin y={{x}^{2}}+\log x+c\]      

    D)                 \[y\sin y=x\log x+c\]

    Correct Answer: A

    Solution :

                       \[\frac{dy}{dx}=\frac{x\log {{x}^{2}}+x}{\sin y+y\cos y}\].                    Separating the variables and integrating         \[\int{(\sin y+y\cos y)dy=\int{(x\log {{x}^{2}}+x)dx}}\]         Þ \[-\cos y+y\sin y+\cos y\]                            \[=\frac{{{x}^{2}}}{2}\log {{x}^{2}}-\int{\frac{{{x}^{2}}}{2}.\frac{1}{{{x}^{2}}}.2xdx+\int{x\,dx+c}}\]         Þ \[y\sin y=\frac{{{x}^{2}}}{2}2\log x-\int{x\,dx+\int{xdx+c}}\]                 Þ \[y\sin y={{x}^{2}}\log x+c\].   


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