Differential Equations, again

[Speedo]

Can anyone point me to a place that decently explains how to do linear nonhomogeneous second-order equations by variation of parameters and method of undetermined coefficients?

My instructor is god awful at explaining this stuff (actually, she doesn't explain it at all) and the book isn't much better. I've spent probably 12+ hours over the weekend and another 2 this morning working on this crap and I still have very little understanding of it. And considering that I have a test on it in about 2 hrs....

 

[Abaddon]

And considering that I have a test on it in about 2 hrs....

I would assume your screwed

 

[Sidhe]

http://www.physicsforums.com/

Huge user base, they wont tell you how to do the equations but they'll show you how to work through them.

Try the homework sections.

Ask the question here, or better still show us a differential and we'll help you work through it?

Well i say we I haven't done the stuff your asking about but there are a few maths P.h.D's in here.

 

[Shaihulud]

Gggahhh! You have better study hard and stop asking advice from here! Its not going to help much in 2 hrs. Check the tutorial question, i assume that the answers are available at the back of the book.

 

[Perfection]

They're not too bad really. All you need to do is find one solution and you've found them all!

To find the single solution just make an assumption that you think will work. For example if you differential equations' non-homogeneous term is 4e^4t guess that one solution is Ae^4t plug it into the differential equation and solve for A. If it's 2x^2+4x+7 guess ax^2+bx+c. (If it has sine or cosine make sure you use both).

To find the other solutions simply solve the associated homogeneous differential equation (set the non-homogeneous equation's non-homogeneous term to zero) and take on the solution to the end.