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# second order ode help watch

1. Hi - i'm new to this forum so bar with me if my formatting is off

I have quite a simple second order ODE but it's been a while...

y''+3y'+2y=5sinx

first i found the CF

L^2 + 3L + 2 = 0

=> y = Ae^-2x + Be^-x

now i need to find the PI...

is it a simple case of setting y=Csinx then subbing into my original equation? when i do that i get cos terms which are hard to lose :s

any help would be good thanks
2. Csinx+Dcosx if the thing you want to end up with is of the form sinx or cosx.
3. Particular integral in the case of sin or cos needs to be

That might work out a little nicer with the algebra...
4. ^ wait i think i've got it.

do i set y=Dsinx + Ccosx?

that gets me D=-5/8 C=15/8

then add PI and CF to get y(total)?

EDIT:thanks guys - i hadn't learnt the joys of refresh yet
EDIT2: does this forum support tex?
5. Hey Boltman, yeh it does support tex (by which I assume you mean LaTeX ;D)

Example:

Solve for y

Just the standard surround your LaTeX by [tex] tags, have a little look here ;D

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