Superposition and variation of parameters

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SUMMARY

The discussion centers on solving the differential equation y'' + 2y' + y = 4t^2 - 3 + (e^-t)/t using the method of variation of parameters. The general solution is identified as c1e^-t + c2te^-t. The user attempts a particular solution of the form y = At^2 + Bt + C + (1/(Dt + E))e^-t but struggles with the differentiation and substitution process. It is concluded that since (1/t)e^-t is not a solution to the homogeneous equation, the method of undetermined coefficients is not applicable, and variation of parameters should be employed to find a specific solution.

PREREQUISITES
  • Understanding of second-order linear differential equations
  • Familiarity with the method of variation of parameters
  • Knowledge of homogeneous and particular solutions
  • Basic skills in differentiation and algebraic manipulation
NEXT STEPS
  • Study the method of variation of parameters in detail
  • Practice solving second-order linear differential equations with non-homogeneous terms
  • Learn about the application of the Wronskian in variation of parameters
  • Explore examples of particular solutions for functions like (1/t)e^-t
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Students and educators in mathematics, particularly those studying differential equations, as well as anyone seeking to deepen their understanding of advanced solution techniques for linear differential equations.

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Homework Statement



y''+2y'+y = 4t^2 - 3 + (e^-t)/t

of course i evaluated the general soltuion to be c1e^-1t + c2te^-1t

but now how do you do the right part? i tried y=At^2+Bt+c+1/(Dt+E)*e^-t as a solution but after differentiating it twice and putting it into the eqaution i got...

(4e^t/Dt+E)-(4De^t/(Dt+E^2))+(2D^2e^t/(Dt+E)^3)+At^2+4At+Bt+2A+2B+C = 4t^2-3+(e^-t)/t

and i don't know what to do with that. i found a=4 and b=0 and c=-11 but that's about all i did, I'm unsure how to find the rest of the letters to complete the probleme

Homework Equations





The Attempt at a Solution

 
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Since (1/t) e-t is NOT one of the solutions one would expect to get as a solution to a homogeneous d.e. with constant coefficients, "undetermined coefficients" will not work. You titled this "superposition and variation of parameters". Have you tried variation of parameters to get a specific solution for the (1/t)e-t?
 

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