Going from this point in Melody's answer....
P(z) = z^4 - z^3 + z^2+ 2
We know that 1 + i is a root....therefore (1 - i) must also be a root.....thus, the resulting polynomial is
[z - ( 1 + i ) ] [ z - (1 - i ) ] =
z^2 -z(1 + i) -z(1-i) + 2 =
z^2 - 2z + 2
Now.....using some polynomial long division, we can determine the other factor
z^2 + z + 1
z^2 - 2z + 2 [ z^4 - z^3 + z^2 + 2 ]
z^4 - 2z^3 + 2z^2
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z^3 - z^2 + 2
z^3 -2z^2 + 2z
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z^2 - 2z + 2
z^2 -2z + 2
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And the two factors are ( z^2 - 2z + 2 ) ( z^2 + z + 1 )
