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The equation \( \dfrac{dy}{dx} = \dfrac{x}{y} \) is solved by

  • A.treating it as exact and finding a potential function
  • B.separating the variables and integrating each side
  • C.an integrating factor depending on x alone
  • D.the substitution \( y = vx \)

Answer: B

Writing it as \( y\,dy = x\,dx \) puts each variable with its own differential, so

\[ \frac{y^{2}}{2} \;=\; \frac{x^{2}}{2} + C \quad \Longrightarrow \quad y^{2} - x^{2} \;=\; k. \]

The solution curves are rectangular hyperbolae. Separation is always worth trying first, since it needs no auxiliary construction at all

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