Differential Equation Method Question

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SUMMARY

The differential equation dy/dx = (y-x)/(y+x) can be approached using substitution, specifically with v = x + y. However, it is crucial to note that the equation is not exact, as the form P(x,y)dy + Q(x,y)dx = 0 does not hold without including the negative factor. The discussion emphasizes the importance of recognizing the exactness of the equation before attempting to solve it.

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  • Understanding of first-order ordinary differential equations (ODEs)
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jofree87
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dy/dx = (y-x)/(y+x)

I am suppose to solve this equation using substitution, but isn't it possible to solve this equation an easier way since it is an exact equation?

(y+x)dy - (y-x)dx = 0
 
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It's not an exact ODE. The form is [tex]P(x,y)dy + Q(x,y) dx = 0[/tex] for exact ODE's, you didn't bring the negative factor in.
 
jofree87 said:
dy/dx = (y-x)/(y+x)

I am suppose to solve this equation using substitution, but isn't it possible to solve this equation an easier way since it is an exact equation?

(y+x)dy - (y-x)dx = 0

[tex]\frac{dy}{dx}=\frac{y-x}{y+x}=\frac{y}{y+x}-\frac{x}{y+x}[/tex]

Use the substitution [tex]v=x+y[/tex].
 

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