Finding a splitting field over Q

In summary, the speaker is trying to construct a splitting field for the polynomial f(x)=x^4-x^3-5x+5 over Q. They first assume a root r and divide f(x) by (x-r). They then discuss checking for obvious integer roots and reducing the expression to (x-1)(x^3-5). They also mention that the roots of x^3-5 may be the cube root of 5 and the product of the cube root of 5 with the first and second powers of a third root of unity.
  • #1
PsychonautQQ
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Homework Statement


I need to construct a splitting field of f(x)=x^4-x^3-5x+5 over Q

Homework Equations

The Attempt at a Solution


So first I will assume r is a root and divide f(x) by (x-r). The quotient came out to be x^3 + (r-1)x^2 + (r^2-r)x + r^3 - r^2 - 5. I am a bit confused what to do now, do i assume another root, call it m perhaps, and do the division again?
 
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  • #2
Always check first for obvious integer roots.

Most obvious is: 0 is a root if and only if there is no constant term.

Next most obvious is: 1 is a root if and only if the sum of the coefficients is zero.
 
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  • #3
Wow, I didn't know that condition for 1 being a root, thanks! I have now reduced my expression to (x-1)(x^3-5). Will the roots of x^3-5 be the cube root of 5, and then the product of the cube root of 5 with the first and second powers of a third root of unity?
 

What is a splitting field over Q?

A splitting field over Q is a field extension of the rational numbers Q that contains all the roots of a given polynomial. It is the smallest field extension that contains all the roots.

Why is it important to find a splitting field over Q?

Finding a splitting field over Q is important because it allows us to fully factorize polynomials and find all their roots. This is essential in many mathematical and scientific fields, such as algebra, number theory, and cryptography.

How do you find a splitting field over Q?

To find a splitting field over Q, you first need to factorize the given polynomial into irreducible factors. Then, you can construct the splitting field by adjoining all the roots of these factors to Q. This can be done by adding one root at a time until all the roots are included in the field.

Can a polynomial have more than one splitting field over Q?

Yes, a polynomial can have multiple splitting fields over Q. This is because there can be different ways to factorize a polynomial into irreducible factors, leading to different sets of roots. However, all splitting fields over Q for a given polynomial will have the same degree over Q.

Are there any applications of finding a splitting field over Q?

Yes, there are many applications of finding a splitting field over Q. Some examples include using splitting fields to solve equations, to prove the existence of certain objects in algebraic geometry, and to encrypt and decrypt messages in cryptography.

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