ODE: Confused about a Homogeneous Eqn question

In summary, the conversation is about a specific problem in calculus where the goal is to show that a given equation is homogeneous, express it in a different form, and solve for a specific variable. The conversation includes a step-by-step explanation of the process and a question about the solution. The summary also highlights the confusion about a specific term in the solution and asks for clarification.
  • #1
hahutzy
10
0

Homework Statement



So the problem goes like this:

Code:
dy/dx = ( x^2 + xy + y^2 ) / x^2
a) Show that it is a homogeneous equation.
b) Let v = y/x and express the eqn in x and v
c) Solve for y

Homework Equations



(Included)

The Attempt at a Solution



Code:
a) dy/dx = ( x^2 + xy + y^2 ) / x^2 * [(1/xy) / (1/xy)]
         = [(x/y) + 1 + (y/x)] / (x/y)
Since RHS is expressed only in terms of y/x, therefore it is homogeneous.

b) v = y/x
   y = vx
   dy/dv = x
   dy/dx = (dy/dv) (dv/dx) = x (dv/dx)
.'.dy/dx = [(x/y) + 1 + (y/x)] / (x/y) becomes
   x (dv/dx) = [(1/v) + 1 + v] / (1/v)
             = v^2 + v + 1
   dx/x = dv/(v^2 + v + 1)

The problem is, when I solve by integrating both sides, I get some gibberish arctan (2v/sqrt(3) + 1)term.
The solution in the book and solved on wolfram alpha is:
arctan (y/x) - ln |x| = c

However, this answer suggests that the equation in b) must've been
dx/x = dv/(v^2 + 1) <- no v term

Which is clearly not the case...

What am I doing wrong??
 
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  • #2
[tex] \frac {dy}{dx} = x \frac {dv}{dx} + v [/tex]
 
  • #3
Random Variable said:
[tex] \frac {dy}{dx} = x \frac {dv}{dx} + v [/tex]

Thank you!
 

FAQ: ODE: Confused about a Homogeneous Eqn question

What is a homogeneous equation?

A homogeneous equation is a type of differential equation where all the terms can be expressed as a function of the dependent variable. In other words, the equation is "homogeneous" because all the terms have the same degree.

How do I know if a differential equation is homogeneous?

To determine if a differential equation is homogeneous, you can check if all the terms can be expressed as a function of the dependent variable. If this is the case, then the equation is homogeneous.

What does it mean for a solution to be homogeneous?

A homogeneous solution is a solution to a homogeneous equation, which means that all the terms in the equation can be expressed as a function of the dependent variable. In other words, the solution will have the same degree as the equation.

What is the difference between a homogeneous and non-homogeneous equation?

The main difference between a homogeneous and non-homogeneous equation is that in a homogeneous equation, all the terms can be expressed as a function of the dependent variable, whereas in a non-homogeneous equation, there is at least one term that cannot be expressed in this way.

How do I solve a homogeneous equation?

To solve a homogeneous equation, you can use the method of separation of variables or the substitution method. Both methods involve manipulating the equation to isolate the dependent variable and then finding a solution that satisfies the equation.

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