I'm beginning to think perhaps is the wrong form..
Hey guys, I thought I had this question solved, wrote it out in final copy and everything and then I realised I'd made a big mistake. Was hoping someone here would be able to give me a few pointers.
a) Solve the initial value problem:
So first I solved homogeneous general solution:
Therefore the solution looks like:
But I only want real answers, so I use complex exponential to achieve:
Where C1 and C2 are real arbitrary constants.
Then I have to solve for inhomogeneous solution. My error was that the first time I did this I took the form to be
However it was pointed out to me that I can't use sine and cosine on their own because they are in the homogeneous general solution. So I think I have to change the form to:
Then I differentiate twice to get
Subbing these in to
Then I equate the co-efficients and get:
By here I think I've done something drastically wrong. If anyone is able to see if I'm even on the right track it would be greatly appreciated. This is quite urgent, but anything will help! Thanks a lot in advance,
Ok thanks for that,
However, I was taught that if a term is in the homogeneous general solution, you cannot use that term in your form for the inhomogeneous solution. And in the case of this I would have to multiply through by t. Why is it valid if does not equal 1, despite the fact that sines and cosines are still present in the general homogeneous solution?
Also, if you wouldn't mind explaining where you got from it would be nice? Is it something that you just derived, or is it a rule of thumb?
This is starting to confuse me :S
I think will work despite it goes against what I was initially taught. And I can sort of accept that, but with the second form you gave:
why is there no omega in the sine and cosine functions?
I derived it and put it into x'' + x and got:
Where would I go from here?