If p in NN is a prime, is xn+px+p^2 irreducible in ZZ[x]?

opositor5t

opositor5t

Answered question

2022-08-09

If x n + p x + p 2 irreducible in Z [ x ] ?

Answer & Explanation

Bryant Liu

Bryant Liu

Beginner2022-08-10Added 15 answers

As you write
x n + p x + p 2 = ( b k x k + + b 0 ) ( c n k x n k + + c 0 )
First, we may assume b k = c n k = 1, and k > 0 , n k > 0. Then mod p, it will give x n = polynomial × polynomial, this forces that p b i , p c j for i k , j n k. Now consider the term of the degree one of the original polynomial, we obtain p x = ( b 0 c 1 + c 0 b 1 ) x, this gives a contradiction if n k > 1 , k > 1
Now if in the case
x n + p x + p 2 = ( x n 1 + b n 2 x n 2 + + b 0 ) ( x + c 0 )
We have c 0 = p , p, thus p or -p is a root of x n + p x + p 2 , but this is not true.

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