A polynomials with coefficients in a field

In summary: But these two factorizations involve four distinct roots, even though the degree of the polynomial is only 2.In summary, the conversation discusses the proof of a polynomial f of degree n with coefficients in a field F having at most n roots in F. The use of induction and the importance of the coefficients being in a field are mentioned. It is also noted that the same proof may not work for an integral domain, as shown by a counterexample.
  • #1
R.P.F.
211
0

Homework Statement



Prove that a polynomial f of degree n with coefficients in a field F has at most n roots in F.


Homework Equations





The Attempt at a Solution



So we could prove this by induction by using a is a root of f if and only if x-a divides f. My question is: why do the coefficients have to be in a field? Shouldn't an integral domain work? Thanks!
 
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  • #2
Once you've proven it for a field, it's easy to prove it for an integral domain.

If you tried to prove it directly for integral domains, it would be trickier -- the field case has fewer details to worry about.
 
  • #3
Hurkyl said:
Once you've proven it for a field, it's easy to prove it for an integral domain.

If you tried to prove it directly for integral domains, it would be trickier -- the field case has fewer details to worry about.

Hmmm...Doesn't the same proof work for an integral domain? I mean the claim that
a is a root of f(x) in R[x] if and only if x-a divides f(x) is true as long as R is an integral domain(or maybe as long as R is a ring?). Then we can just use induction.
 
  • #4
It's not too hard to find a counterexample to the case of general rings.

For example, consider the polynomial x2 - 1 with coefficients in the ring of integers modulo 8. It factors in two ways:
x2-1 = (x-1)(x-7) = (x-3)(x-5)​
 

FAQ: A polynomials with coefficients in a field

What is a polynomial with coefficients in a field?

A polynomial with coefficients in a field is a mathematical expression made up of variables, constants, and coefficients from a specific field. The field provides the set of numbers from which the coefficients can be chosen, and the variables represent unknown quantities. Examples of fields include the real numbers, complex numbers, and rational numbers.

How is a polynomial with coefficients in a field different from a regular polynomial?

A regular polynomial can have coefficients from any set of numbers, while a polynomial with coefficients in a field only uses coefficients from a specific field. This restriction allows for a more precise and generalized understanding of polynomials, as well as applications in various mathematical fields such as abstract algebra and number theory.

What are some common fields used in polynomials?

Some common fields used in polynomials include the real numbers, complex numbers, rational numbers, and finite fields such as the integers modulo a prime number. Other fields used in polynomials include algebraic number fields, function fields, and polynomial rings.

How are polynomials with coefficients in a field used in mathematics?

Polynomials with coefficients in a field have various applications in mathematics, including algebraic geometry, number theory, and signal processing. They are also used in constructing finite fields, factoring algorithms, and solving systems of equations. Additionally, they play a key role in computer science and coding theory.

Can polynomials with coefficients in a field be graphed?

Yes, polynomials with coefficients in a field can be graphed just like regular polynomials. The only difference is that the coefficients are chosen from a specific field instead of any set of numbers. This means that the graph may have different properties, such as being defined over a finite set of points instead of a continuous line. However, the fundamental concepts of graphing, such as finding roots and intercepts, still apply.

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