Proving the superposition principle

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Homework Help Overview

The discussion revolves around proving the superposition principle for linear homogeneous equations, specifically focusing on the solutions of the ordinary differential equation (ODE) y' + p(t)y = 0. The original poster attempts to understand how the sum of two solutions and a scalar multiple of a solution also yield solutions.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the implications of substituting the sum of solutions into the ODE and question the differentiation properties that support the superposition principle. There is also inquiry into proving the principle for scalar multiples of solutions.

Discussion Status

The discussion has progressed with some participants providing guidance on how to approach the proof by using the properties of the original solutions. The original poster has expressed understanding after initial confusion, and further questions about extending the proof to combinations of solutions have been raised.

Contextual Notes

Participants are working within the constraints of proving properties of solutions to a specific type of linear ODE and are exploring the implications of the superposition principle without providing complete solutions.

bleucat
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Homework Statement



Hi everyone.
I am trying to prove the superposition principle for linear homogeneous equations, which states that if u(t) and w(t) are solutions to y' + p(t)y = 0, then u(t) + w(t) and k(u(t)) are also solutions for any constant k.


The Attempt at a Solution


I substituted (u + w) in for y, but how does that help me?

Thanks in advance for the help!
 
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Use the fact that u(t),w(t) satisfy the ODE.
 
As in, what differentiation property makes u + w a solution if u, w are?
 
The statement u(t),w(t): solutions of the ODE means

u'(t)+p(t)\,u(t)=0, \, w'(t)+p(t)\,w(t)=0

Put y'(t)=u'(t)+w'(t) in the original ODE and use the above equations.
 
Hah, I got it. That wasn't bad at all.
Thanks!
 
Now, can you do it for ku(t)? And, can you prove that those two together show that
au(t)+ bv(t) is a solution for any numbers a, b, as long as u(t) and v(t) are solutions?
 

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