Solving Exact Diff. Eq: Finding Integral Curves

  • Thread starter Thread starter fluidistic
  • Start date Start date
  • Tags Tags
    Curves Integral
Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
2 replies · 2K views
fluidistic
Gold Member
Messages
3,934
Reaction score
286

Homework Statement


Find the solution to [itex]y'=\frac{y+x}{y-x}[/itex] and graph the integral curves.

Homework Equations


Exact differential equation.

The Attempt at a Solution


I noticed it's an exact differential equation, I solved it implicitely. I reached that [itex]\frac{y^2 (x)}{2}-\frac{x^2}{2}-yx=\text{constant}[/itex]. I've looked into wikipedia about the integral curves but I don't really know how to find them here. If I understood well, an integral curve is a solution to the DE, so here it would be any y(x) that satisfies the DE. But here I can't get y(x) explicitely, so how do I graph y(x)?... Any idea is welcome!
 
Physics news on Phys.org
HallsofIvy said:
Choose a number of specific values for the constant and graph those curves.

Ah I see, thank you very much. I graph point per point, maybe I'm missing an obvious curve or something.
I take C=1. I set x=0 and I get [itex]y=\pm \sqrt 2[/itex]. I graph this in the x-y plane. Now I set x=2 and I get a quadratic equation for y, which yields [itex]y= 2 \pm \sqrt {10}[/itex]. So for a fixed C, there are 2 curves; maybe parabolas or hyperbolas.