<s>[INST] Simplify $ z^4+z^2+1$ 
$$ z^4+z^2+1$$ 

I'm trying to get this form: $(z^2+z+1)(z^2-z+1)$ but don't know how.
I tried: $z^2(z^2+1)+1$
 [/INST] We have $z^4 + 2z^2 - z^2 + 1 = 0$
$z^4 + 2z^2 + 1 - z^2 = 0$
$(z^2 + 1)^2 - z^2 = 0$
$(z^2 + 1 + z)(z^2 + 1 - z)= 0$
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