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Post Reopened by YCor, j.c., Yemon Choi, Dima Pasechnik, Stefan Kohl
Slightly rephrased. The question was unfairly closed and should be reopened.
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YCor
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IfFor $n\ge 1$, let $g(x_1,x_2,\ldots,x_n)$ isbe an irreducible homogeneoushomogeneous polynomial in $n$ variables over a field $k$ and $f(x)$ is an irreducible polynomial of $k[x]$, is. Is $f(g(x_1,x_2,\ldots,x_n))$ alsonecessarily irreducible?

For instance this holds when $n=1$ (since then $g(x_1)=\lambda x_1$), or when $f$ has degree 1 (by a simple argument).

If $g(x_1,x_2,\ldots,x_n)$ is an irreducible homogeneous polynomial in $n$ variables over a field $k$ and $f(x)$ is an irreducible polynomial of $k[x]$, is $f(g(x_1,x_2,\ldots,x_n))$ also irreducible?

For $n\ge 1$, let $g(x_1,x_2,\ldots,x_n)$ be an irreducible homogeneous polynomial in $n$ variables over a field $k$ and $f(x)$ an irreducible polynomial of $k[x]$. Is $f(g(x_1,x_2,\ldots,x_n))$ necessarily irreducible?

For instance this holds when $n=1$ (since then $g(x_1)=\lambda x_1$), or when $f$ has degree 1 (by a simple argument).

Post Closed as "Not suitable for this site" by YCor, abx, Ian Morris, Dima Pasechnik, Stefan Kohl

If g(x_1,x_2,...,x_n)$g(x_1,x_2,\ldots,x_n)$ is an irreducible homogeneous polynomial in n$n$ variables over a field k$k$ and f(x)$f(x)$ is an irreducible polynomial of k[x]$k[x]$, is f(g(x_1,x_2,...x_n))$f(g(x_1,x_2,\ldots,x_n))$ also irreducible?

If g(x_1,x_2,...,x_n) is an irreducible homogeneous polynomial in n variables over a field k and f(x) is an irreducible polynomial of k[x], is f(g(x_1,x_2,...x_n)) also irreducible?

If $g(x_1,x_2,\ldots,x_n)$ is an irreducible homogeneous polynomial in $n$ variables over a field $k$ and $f(x)$ is an irreducible polynomial of $k[x]$, is $f(g(x_1,x_2,\ldots,x_n))$ also irreducible?

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Irreducibility of a polynomial

If g(x_1,x_2,...,x_n) is an irreducible homogeneous polynomial in n variables over a field k and f(x) is an irreducible polynomial of k[x], is f(g(x_1,x_2,...x_n)) also irreducible?