Machine-translated by Google. Questions are authored in English.
Top

Discussion

The general solution of the differential equation \(ydx - xdy = y^{2}(xdy + ydx)\) is

  • A.\(\frac{y}{x} = xy + C\)
  • B.\(\frac{x}{y^{2}} = xy + C\)
  • C.\(\frac{y}{x^{2}} = xy + C\)
  • D.\(x + y = xy + C\)
  • E.\(\frac{x}{y} = xy + C\)

Answer: E

The general solution is \(\frac{x}{y} = xy + C\).

Recognise the two exact differentials: \(xdy + ydx = d(xy)\) and \(\frac{ydx - xdy}{y^{2}} = d\left(\frac{x}{y}\right)\). Divide the equation by \(y^{2}\):

\[ \begin{aligned} \frac{ydx - xdy}{y^{2}} &= xdy + ydx \\ d\left(\frac{x}{y}\right) &= d(xy) \end{aligned} \]

Integrating, \(\frac{x}{y} = xy + C\). \(\frac{y}{x}\) has the quotient upside down, since \(d\left(\frac{y}{x}\right) = \frac{xdy - ydx}{x^{2}}\), with the opposite sign and \(x^{2}\) underneath.

No comment is present. Be the first to comment.
Loading…

Post your comment

Please log in or register to post a comment.