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Update 2023-11-11-linalglinconstcoef.md
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smashmath committed Nov 12, 2023
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importance: 1
tags: best
category: differential-equations
authors:
authors:
- name: Taylor Grant
url: ""
affiliations:
Expand Down Expand Up @@ -189,7 +189,9 @@ We can prove that \eqref{kerda} actually generalizes to $$n$$th order equations

Suppose $$p(x)$$ is a second degree polynomial. Then $$p(x)=(x-a)q(x)$$ where $$q(x)$$ is a degree one polynomial (this is guaranteed by the fundamental theorem of algebra, meaning $$a$$ can be complex). Hence,

$$p(D)y=0\implies (D-a)q(D)y=0\implies q(D)y\in\ker(D-a)$$
$$p(D)y=0\implies (D-a)q(D)y=0$$

$$\implies q(D)y\in\ker(D-a)$$

\eqref{kerda} then tells us that $$q(D)y=c_2e^{at}$$. We know we can find a particular solution to $$q(D)y=e^{at}$$ (which we will call $$y_2$$) by using an [integrating factor](../integratingfactor/){:target="_blank"}, since it's first order$$^{[1]}$$.

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