tag removed – Solve a cubic equation of one variable with parameters!

x^3 + Cos((Theta))x^2 + E^(I(Theta))Cos((Theta))x + E^(
I
(Theta))=0
and
x^3 + I
Sin((Theta))x^2 + E^(I(Theta))ISin((Theta))x – E^(
I
(Theta))=0
They come from these two matrices, and I’m trying to figure out its eigenvectors, but I can’t figure out its eigenvalues.
( {
{0, 0, E^(I*(Theta))},
{-Cos((Theta)), -ISin((Theta)), 0},
{-I
Sin((Theta)), -Cos((Theta)), 0}
} )
and
( {
{-Cos((Theta)), -ISin((Theta)), 0},
{0, 0, E^(I
(Theta))},
{-I*Sin((Theta)), -Cos((Theta)), 0}
} )

Both equations are written in the corresponding code, which can be opened with the appropriate mathematical software to view the original format.
Thanks!