Solving Exact Diff. Eq: Finding Integral Curves

In summary, the conversation discusses finding the solution to the exact differential equation y'=(y+x)/(y-x), as well as graphing the integral curves. The solution is implicit and involves a constant, which can be graphed by choosing specific values for the constant and plotting the corresponding curves. The conversation also mentions using point-by-point graphing and obtaining multiple curves for a fixed constant.
  • #1
fluidistic
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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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  • #2
Choose a number of specific values for the constant and graph those curves.
 
  • #3
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.
 

1. What is the purpose of finding integral curves in solving exact differential equations?

The purpose of finding integral curves is to determine the general solution to a given exact differential equation. Integral curves are curves that satisfy the differential equation at every point, and finding them allows us to find the solution that satisfies the initial conditions.

2. How do you find integral curves for an exact differential equation?

To find integral curves, we first need to ensure that the given differential equation is exact. This means that the partial derivatives of the equation with respect to the variables must be equal. Then, we can use the method of integrating factors or the method of separation of variables to find the general solution and subsequently, the integral curves.

3. Can there be multiple integral curves for a given exact differential equation?

Yes, there can be multiple integral curves for a given exact differential equation. This is because the general solution to an exact differential equation contains an arbitrary constant, which allows for an infinite number of integral curves that satisfy the equation.

4. How do you determine which integral curve satisfies a given set of initial conditions?

To determine which integral curve satisfies a given set of initial conditions, we substitute the initial values into the general solution. This will give us a specific solution that satisfies the initial conditions and represents a specific integral curve.

5. Are there any techniques for visualizing integral curves?

Yes, there are techniques for visualizing integral curves. One method is to use slope fields or direction fields, which involve plotting small line segments at different points on the integral curve to show the direction of the curve at that point. Another method is to use computer software to plot the integral curves for a given exact differential equation.

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