Question

When finding the particular solution to x'' + 4x = sin(x) + cos(x) can I use undetermined coefficients?

Answer 1

I think so.
Though, are you sure that's x''+4x and not y''+4y?

Answer 2

Probably, I interchange them constantly.

If you do you undetermined coeff, then are you familiar with the process of spiting up the right side of the equation to make the method of finding the particular easier?

Answer 3

O, wait the equation is

x'' + 4x = sin(t) + cos(t)

Answer 4

Ah, ok. Yes, You can assume that the particular is some combination of sines and cosines, such as Asin(t) + Bcos(t).

Answer 5

See http://tutorial.math.lamar.edu/Classes/DE/UndeterminedCoefficients.aspx for more examples.