I want to show that the following polynomial is irreducible in Z[X]: f(X)=X^4−4X^3−4X^2+16X−8.

Widersinnby7

Widersinnby7

Answered question

2022-11-06

I want to show that the following polynomial is irreducible in Z [ X ]
f ( X ) = X 4 4 X 3 4 X 2 + 16 X 8.

Answer & Explanation

Quinten Cervantes

Quinten Cervantes

Beginner2022-11-07Added 13 answers

Let X = 2 y. Substitute and divide through by 8. We get an expression of shape P ( y ) = 2 y 4 + a 3 y 3 + a 2 y 2 + a 1 y 1, where the a i are divisible by 2.
Let y = 1 z , and consider the polynomial Q ( z ) = z 4 P ( 1 / z ) = z 4 + a 1 z 3 + a 2 z 2 + a 3 z + 2
This is irreducible over the rationals if and only if P(y) is. Now use the Eisenstein Criterion.

Do you have a similar question?

Recalculate according to your conditions!

Ask your question.
Get an expert answer.

Let our experts help you. Answer in as fast as 15 minutes.

Didn't find what you were looking for?