When and How to Solve ODEs: Clarity for Confused Students

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SUMMARY

This discussion clarifies the appropriate methods for solving ordinary differential equations (ODEs). The consensus is to use the trial function y=e^mx for ODEs with constant coefficients, while y=x^m is suitable for Cauchy-Euler equations. The derivatives of e^{ax} yield similar forms, making them effective for linear differential equations with constant coefficients. In contrast, the derivatives of x^a produce varying powers, which align with linear differential equations that have powers of x as coefficients.

PREREQUISITES
  • Understanding of ordinary differential equations (ODEs)
  • Familiarity with trial functions in differential equations
  • Knowledge of Cauchy-Euler equations
  • Basic calculus, specifically differentiation techniques
NEXT STEPS
  • Study the characteristics of Cauchy-Euler equations
  • Learn about linear differential equations with constant coefficients
  • Explore the method of undetermined coefficients for ODEs
  • Practice solving ODEs using both trial functions y=e^mx and y=x^m
USEFUL FOR

Students and educators in mathematics, particularly those focused on differential equations, as well as anyone seeking clarity on the application of different trial functions in solving ODEs.

ABearon
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TL;DR
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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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 !
 
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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The derivatives of e^{ax} are all of the form e^{ax} again. That is why they are solutions to linear differential equations with constant coefficients. The derivatives of x^a are of the form x^b with b< a. That is why the are solutions to linear differential equations with powers of x as coefficients.
 
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