The closure property for polynomials states that the sum, difference, and product of two polynomials is also a polynomial. However, the closure property does not hold for division, as dividing two polynomials does not always result in a polynomial. Consider the following example: Let P(x)=x2+1 and Q(x)=x.
Closure property It says that when we sum up or multiply any two natural numbers, it will always result in a natural number. Here, 3, 4, and 7 are natural numbers. So this property is true. Here, 5,6, and 30 are natural numbers.
The field F is algebraically closed if and only if it has no proper algebraic extension. If F has no proper algebraic extension, let p(x) be some irreducible polynomial in Fx. Then the quotient of Fx modulo the ideal generated by p(x) is an algebraic extension of F whose degree is equal to the degree of p(x).
The field F is algebraically closed if and only if every polynomial p(x) of degree n ≥ 1, with coefficients in F, splits into linear factors. In other words, there are elements k, x1, x2, ..., xn of the field F such that p(x) = k(x − x1)(x − x2) ⋯ (x − xn).
Closure Property: When something is closed, the output will be the same type of object as the inputs. For instance, adding two integers will output an integer. Adding two polynomials will output a polynomial. Addition, subtraction, and multiplication of integers and polynomials are closed operations.
Definition 1. A field K is algebraically closed if it contains a root to every non-constant polynomial in the ring KX of polynomials in one variable with coefficients in K.
We say that E is an algebraic closure of F if E is an algebraic extension of F, and E is algebraically closed. Some examples: C is an algebraic closure of R. By the Fundamental Theorem of Algebra, C is algebraically closed; and since the extension has finite degree C : R = 2, it is algebraic.
A field F is algebraically closed if and only if every nonconstant poly- nomial f(x) ∈ Fx is a product of linear polynomials. f(x)=(x − α)g(x), g(x) ∈ Fx. If g(x) is not constant, we can find a β ∈ F such that g(β)=0, hence f(x)=(x − α)(x − β)h(x) h(x) ∈ Fx.
All transcendental extensions are of infinite degree. This in turn implies that all finite extensions are algebraic. The converse is not true however: there are infinite extensions which are algebraic. For instance, the field of all algebraic numbers is an infinite algebraic extension of the rational numbers.