Differential equations - undetermined coefficients

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SUMMARY

The discussion focuses on solving the differential equation y'' + 2y' + 5y = e^x * sin(x) using the method of undetermined coefficients. The characteristic equation is derived as r^2 + 2r + 5 = 0, yielding complex roots r1 = -1 + 2i and r2 = -1 - 2i, leading to the homogeneous solution y_h = c1 * e^(-x) cos(2x) + c2 * e^(-x) * sin(2x). The participant seeks clarification on applying the undetermined coefficients method to the non-homogeneous part e^x * sin(x), which presents a challenge due to its complexity.

PREREQUISITES
  • Understanding of differential equations, specifically second-order linear equations.
  • Familiarity with the method of undetermined coefficients.
  • Knowledge of complex numbers and their application in solving characteristic equations.
  • Basic skills in manipulating exponential and trigonometric functions.
NEXT STEPS
  • Study the method of undetermined coefficients in detail, focusing on its application to non-homogeneous equations.
  • Review complex roots in differential equations and their implications for homogeneous solutions.
  • Explore examples of solving differential equations with e^x and trigonometric functions as non-homogeneous terms.
  • Practice deriving particular solutions for various forms of non-homogeneous differential equations.
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Students studying differential equations, educators teaching advanced mathematics, and anyone seeking to master the method of undetermined coefficients in solving complex differential equations.

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Homework Statement


Find a particular solution of y'' + 2y' + 5y = e^x * sin(x)

Homework Equations


The Attempt at a Solution


Characteristic equation: r^2 + 2r + 5 = 0. Through quadratic formula, r1 = -1+2i and r2 = -1-2i, so my homogeneous equation is y_h = c1 * e^(-x) cos(2x) + c2 * e^(-x) * sin(2x).
Now, I need to use the undetermined coefficients method. How? I'm trying to figure out what exactly this undetermined coefficients method is, as my notes from lecture are confusing. And the e^x * sin(x) on the right looks like it would make things difficult.

I'd appreciate any guidance in the right direction, thanks!
 
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hi mbradar2! :smile:

(try using the X2 and X2 icons just above the Reply box :wink:)

there's a good guide at http://en.wikipedia.org/wiki/Undetermined_coefficients" , beginning …
the method of undetermined coefficients, otherwise known as the Lucky Guess Method …

:biggrin:
 
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