Inhomogenous ODEs, Particular solutions question

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1.The position of a particle x(t) obeys the following differential equation

d^2x/dt^2 + 4(dx/dt) + 3x = (3t/2) -4

If at t=0, both x=0 and dt/dx=0, find x(t)






Attempt at solution
I've found the homogeneous solution to be y=Aexp(-3x) + Bexp(-x), and know how to find x(t) given boundary conditions, but I'm having trouble finding the particular solution. I know you have to use g(x) where g(x) is the RHS of the equation, but when I try using Yp=r exp(mu x) or a combination of factors of x, I get a load of rubbish. Can anyone please help?
 
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If you look at the form of the RHS, you might guess that a particular solution would have the form x(t)=a*t+b. Put that into the equation at try to find a and b. You first try at finding a particular solution should always be to try and guess what it could be and then prove yourself right.
 
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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