When and How to Solve ODEs: Clarity for Confused Students

In summary, the use of different trial functions, such as e^{mx} and x^m, depends on the type of differential equation being solved. For equations with constant coefficients, e^{mx} is often a useful choice, while for Cauchy-Euler equations with variable coefficients, x^m may be a better option. The properties of these functions and their derivatives make them suitable for solving different types of differential equations.
  • #1
ABearon
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TL;DR Summary
when to use e^mx and x^m
I know how to solve ODEs using both methods. The problem I'm having is knowing when to use one and not the other. If someone could help clarify this for me. I can't find the correct section in my textbook.
 
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  • #2
Hello ABearon, :welcome: !

Bit hard to answer without examples. Perhaps you can provide an example for yourself by going the other way: try to compose an exercise where ##x^m## is a useful trial function and another example where ##e^{mx}## is a good choice. Not too hard: simply differentiate and see what kind of DE you can make form the result !
 
  • #3
BvU said:
Hello ABearon, :welcome: !

Bit hard to answer without examples. Perhaps you can provide an example for yourself by going the other way: try to compose an exercise where ##x^m## is a useful trial function and another example where ##e^{mx}## is a good choice. Not too hard: simply differentiate and see what kind of DE you can make form the result !
I think i figured it out. We're supposed to use y=e^mx when the ode has constant coefficients (a, b, c) and y=x^m for Cauchy-Euler equations, which are ODEs but the terms have have a-sub-n(x^n)(d^n y/dx^n)
 
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  • #4
The derivatives of [itex]e^{ax}[/itex] are all of the form [itex]e^{ax}[/itex] again. That is why they are solutions to linear differential equations with constant coefficients. The derivatives of [itex]x^a[/itex] are of the form [itex]x^b[/itex] with b< a. That is why the are solutions to linear differential equations with powers of x as coefficients.
 
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1. What are ODEs?

ODEs, or ordinary differential equations, are mathematical equations that involve one or more unknown functions and their derivatives. They are used to model a wide range of phenomena in science and engineering.

2. When do we need to solve ODEs?

ODEs are used to describe the behavior of dynamic systems, such as population growth, chemical reactions, and motion of objects. Therefore, they need to be solved whenever we want to understand the behavior of a system over time.

3. How do we solve ODEs?

There are various methods for solving ODEs, including analytical methods, such as separation of variables and integrating factors, and numerical methods, such as Euler's method and Runge-Kutta methods. The choice of method depends on the complexity of the ODE and the desired level of accuracy.

4. What are some common mistakes when solving ODEs?

Some common mistakes when solving ODEs include forgetting initial conditions, making algebraic errors, and using incorrect methods. It is important to carefully check the problem and the solution to avoid these mistakes.

5. How can I improve my understanding of solving ODEs?

Practice and understanding the underlying concepts are key to improving your understanding of solving ODEs. It is also helpful to seek out additional resources, such as textbooks, online tutorials, and practice problems, to supplement your learning.

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