Method of Undetermined Coefficients

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Homework Statement
Decide whether or not the method of indetermined coefficients can be applied to find a particular solution of the given equation:

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The attempt at a solution
I think the answer is yes, because the equation is of the form: a\ddot{y}+b\dot{y}+cy=F(t)where F(t) is the sum or product of polynomials, exponentials, sines, cosines.

Am I correct?
 
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Yes it can, you can also factor out the 4x to make it easier since you know what sin2x+cos2 is equal to.
 
Oh so I can replace sin2x+cos2x with 1, which gives me a RHS of simply 4x?
 
Yep.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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