Solving First Order Linear ODE: dy/dx = y/x + tan(y/x)

In summary, the conversation discusses how to solve the differential equation dy/dx = y/x + tan(y/x). The participants consider various methods such as separation of variables and substitution, ultimately determining that a substitution of u = y/x is the most effective approach. They also clarify that this substitution method is not limited to homogeneous equations.
  • #1
whatisreality
290
1

Homework Statement


Solve dy/dx = y/x + tan(y/x)

Homework Equations

The Attempt at a Solution


Not separable, as far as I can tell. It's not homogeneous, since for the tan term f(λx,λy) = tan(λy/λx) = tan(y/x) ≠ λtan(y/x). It's also not of the form dy/dx + P(x)y = Q(x), because I don't think Q(x) should involve y. And that completes the list of methods I know, none of which I can use! How do you solve this?! Is there a substitution I should make?
 
Physics news on Phys.org
  • #2
Even though this is not homogeneous, seeing that "y/x" my first thought would be to try the substitution u= y/x.

Then y= xu so that dy/dx= u+ x du/dx. The differential equation becomes u+ x du/dx= u+ tan(u) so that x du/dx= tan(u).

That is separable.
 
  • #3
You could try making a change in the dependent variable, from [itex]y[/itex] to [itex]u[/itex], where [itex]u= y/x[/itex]
 
  • #4
OK, that substitution works! I thought it was only for homogeneous equations. Thanks :)
 

1. What is a first order linear ODE?

A first order linear ODE (ordinary differential equation) is a mathematical equation that involves a single independent variable and its first derivative, with the dependent variable appearing in a linear manner. It can be written in the form: dy/dx + P(x)y = Q(x), where P(x) and Q(x) are functions of x.

2. How do you solve a first order linear ODE?

To solve a first order linear ODE, you can use the method of separation of variables, where you separate the variables and then integrate both sides. Another method is to use an integrating factor, which is a function that helps to simplify the equation. You can also use the method of variation of parameters, where you assume a solution of the form y = u(x)v(x) and solve for u(x) and v(x).

3. What are the applications of first order linear ODEs?

First order linear ODEs have many applications in science and engineering, such as in physics, chemistry, biology, economics, and more. They are used to model and predict various phenomena, such as population growth, chemical reactions, heat transfer, and circuit analysis.

4. Can a first order linear ODE have multiple solutions?

Yes, a first order linear ODE can have multiple solutions. This is because the general solution of a first order linear ODE contains an arbitrary constant, which can take on different values depending on the initial conditions. Therefore, there can be infinite solutions to a first order linear ODE.

5. What are the initial conditions in a first order linear ODE?

The initial conditions in a first order linear ODE refer to the values of the dependent variable and its derivative at a specific point, usually denoted as x = a. These values are necessary to find the particular solution of the ODE, as the general solution contains an arbitrary constant that can be determined by the initial conditions.

Similar threads

  • Calculus and Beyond Homework Help
Replies
8
Views
763
  • Calculus and Beyond Homework Help
Replies
19
Views
776
  • Calculus and Beyond Homework Help
Replies
2
Views
1K
  • Calculus and Beyond Homework Help
Replies
21
Views
842
  • Calculus and Beyond Homework Help
Replies
2
Views
260
  • Calculus and Beyond Homework Help
Replies
11
Views
962
  • Calculus and Beyond Homework Help
Replies
1
Views
829
  • Calculus and Beyond Homework Help
Replies
7
Views
708
  • Calculus and Beyond Homework Help
Replies
4
Views
925
  • Calculus and Beyond Homework Help
Replies
3
Views
572
Back
Top