Laplace transform w/ partial fraction

SpartanArt
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Homework Statement


solve the following initial value problem using Laplace transforms
y"+2y'+y=(8/3)cos(2t)-2sin(2t)
y(0)=1
y'(0)=7/3


Homework Equations


L[d^2y/dt^2]=s^2Y-sy(0)-y'(0)
L[dy/dt]=sY-y(0)
L[coswt]=s/(s^2+w^2)
L[sinwt]=w/(s^2+w^2)


The Attempt at a Solution



so far: Y={s^3+(13/3)s^2+(20/3)s+(40/3)}/{(s^2+4)(s^2+2s+1)}
need help turning denominator into partial fraction.
Thanks!
 
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thanks a lot!
 
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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