Solving DE Homework: Non-Unique PI?

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SUMMARY

The discussion centers on solving the differential equation D²(y) + 5Dy + 4y = cos(2x) and determining the uniqueness of the particular integral (PI). The general solution provided is y = C1 exp(-x) + C2 exp(-4x) + (1/10)cos(2x). Participants confirm that particular integrals are not unique, emphasizing the need to differentiate to verify solutions. The discussion highlights the importance of understanding the definition of a particular integral in the context of differential equations.

PREREQUISITES
  • Understanding of differential equations, specifically second-order linear equations.
  • Familiarity with the concept of particular integrals in the context of differential equations.
  • Knowledge of differentiation techniques to verify solutions.
  • Basic understanding of exponential functions and trigonometric identities.
NEXT STEPS
  • Review the definition and properties of particular integrals in differential equations.
  • Study the method of undetermined coefficients for finding particular integrals.
  • Learn about the uniqueness theorem for solutions of linear differential equations.
  • Practice solving various second-order linear differential equations with non-homogeneous terms.
USEFUL FOR

Students studying differential equations, educators teaching advanced mathematics, and anyone interested in the nuances of particular integrals and their uniqueness in differential equations.

neelakash
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Homework Statement



Given DE is D^2(y)+5Dy+4y=cos 2x ...where D=>(dy/dx)

We are to find the general solution.(I have done it already)
Is the particular integral unique?If not,find another PI and show that the general solution is the same for all PI.

Homework Equations


The Attempt at a Solution



I did the first part and got the general solution as

y=C1 exp(-x)+C2 exp(-4x)+(1/10)cos 2x

I cannot understand why the PI would be non-unique?Can anyone please check if I am correct in having that answer?
 
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?? You might want to check the definition of "particular integral"! They are never unique.

As far as checking is concerned, all you have to do is differentiate! Did you notice that if y= (1/10)cos(2x) then Dy= (1/5)sin(2x) so 5 Dy= sin(2x). How are you going to get rid of that sin(2x) on the left side of the equation?
 

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