Find a minimal polynomial of element

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Let $\alpha \in \mathbb{C}$ be a root of polynomial $z^3+z+3$

How can I find a minimal polynomial of $\alpha - \alpha^2$ over $\mathbb{Q}$?

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One way to do this is to set $y=z-z^2$ and eliminate $z$ using $z^3+z+3=0$.

Note: The first equation enables you to reduce the second to an expression linear in $z$. Then express $z$ in terms of $y$ and feed into the first equation.