J & K CET Engineering J and K - CET Engineering Solved Paper-2005

  • question_answer
    If c is an arbitrary constant, then the general solution   of   the   differential   equation  \[ydx-xdy=xy\,\,dx\]is given by

    A)  \[y=cx{{e}^{-x}}\]

    B)  \[y=cy{{e}^{-x}}\]

    C)  \[y+{{e}^{-x}}=cx\]    

    D)  \[y{{e}^{x}}=cx\]

    Correct Answer: D

    Solution :

    Given, \[ydx-xdy=xydx\] \[\Rightarrow \] \[ydx-xydx=xdy\] \[\Rightarrow \] \[y(1-x)dx=xdy\] \[\Rightarrow \] \[\left( \frac{1-x}{x} \right)dx=\frac{dy}{y}\] \[\Rightarrow \] \[\left( \frac{1}{x}-1 \right)dx=\frac{1}{y}dy\] On integrating, we get \[\log x-x=\log y-\log c\] \[\Rightarrow \] \[x=\log \frac{xc}{y}\] \[\Rightarrow \] \[{{e}^{x}}=\frac{xc}{y}\] \[\Rightarrow \] \[y{{e}^{x}}=xc\]


You need to login to perform this action.
You will be redirected in 3 sec spinner