Lets work over the finite field $\mathbb{F}_p$ for a prime $p$. Consider a monic irreducible polynomial $f(X)=X^3+aX^2+bX+c$ in $\mathbb{F}_p[X]$. Let $x$ be a root of $f(x)=0$ (say, in the closure of $\mathbb{F}_p$). Consider another different monic irreducible polynomial $g(Y)=Y^3+AY^2+BY+C$ in $\mathbb{F}_p[Y]$. Let $y$ be a root of $g(Y)=0$ again in the same closure.
How do we explicity relate $x$ and $y$? Can we express $y$ as a polynomial in $x$ with coefficients from $\mathbb{F}_p$?
I know that the field extension $\mathbb{F}_{p^3}$ which can be realized as $\mathbb{F}_p[X]/f$ contains $x$ and $y$ (as it contains every root of every irreducible of degree $3$), so $y$ should be expressible in the form
$$y=\alpha x^2+ \beta x +\gamma$$
for some $\alpha, \beta, \gamma \in \mathbb{F}_p$.
But this is what I am trying to establish, without using the uniqueness of $\mathbb{F}_{p^3}$ or it being the splitting field of $X^{p^3}-X$. I would prefer not using any non-trivial facts about finite fields here. My aim is to show that every cubic irreducible has a root in the specific extension $\mathbb{F}_p[X]/f$, and I want to do this by explicitly obtaining a dependence of the form $y=\alpha x^2+ \beta x +\gamma$ whenever $y$ satisfies $y^3+Ay^2+By+C=0$.
Is there some algebraic expression or algorithm to find $\alpha, \beta, \gamma$? Something on the lines of resultants maybe.
I was thinking of considering the ideal $
(This has now been cross-posted to MathOverflow: https://mathoverflow.net/questions/243458/algebraic-dependence-of-irreducibles-in-a-finite-field)
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