partial fraction expansion with null pole and null zero and inverse laplace

The differential equation

?̈(?) + ?(?) − ?(?) = 0, ?(0) = 1, ?̇(0) = −1, ?(?) = ?, ? ≥ 0

transformed according to Laplace gives

Y(s) = (s^3-s^2+1)/s^2/(s^2+1).

Performing the partial fraction expansion

r =

0.5000 + 1.0000i

0.5000 - 1.0000i

0.0000 + 0.0000i how can I perform the pfe and inverse laplace of this?

1.0000 + 0.0000i

p =

0.0000 + 1.0000i

0.0000 - 1.0000i

0.0000 + 0.0000i how can I perform the pfe and inverse laplace of this?

0.0000 + 0.0000i

k =

[]

and applying the inverse Laplace transform, we

obtain

y(t) = 2.236cos(t+1.1071) + t, t>=0

from where it comes this + t?