Solving Exact Diff. Eq: Finding Integral Curves

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SUMMARY

The discussion focuses on solving the exact differential equation y'=(y+x)/(y-x) and finding its integral curves. The user successfully identifies the equation as exact and derives the implicit solution \(\frac{y^2 (x)}{2}-\frac{x^2}{2}-yx=\text{constant}\). To graph the integral curves, the user is advised to select specific constant values and calculate corresponding y-values, leading to the identification of multiple curves, including parabolas or hyperbolas, based on chosen constants.

PREREQUISITES
  • Understanding of exact differential equations
  • Familiarity with implicit function solutions
  • Knowledge of graphing techniques in the x-y plane
  • Basic calculus concepts, including derivatives and integrals
NEXT STEPS
  • Explore methods for graphing implicit functions
  • Learn about the properties of integral curves in differential equations
  • Study the classification of conic sections, specifically parabolas and hyperbolas
  • Investigate numerical methods for approximating solutions to differential equations
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Students and educators in mathematics, particularly those studying differential equations, as well as anyone interested in the graphical representation of mathematical solutions.

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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!
 
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Choose a number of specific values for the constant and graph those curves.
 
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.
 

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