What is the common factor of (a + 3) (A-3)?

What is the common factor of (a + 3) (A-3)?

There is no "common factor" here. Factorization. In the decomposed polynomials, each item has the same factor. It is called "common factor" first proposed. It is a method of factorization. Not all polynomials have common factor
For polynomials without common factor, other methods should be used to decompose the factor
（a+3)(a-3)=a^2-9.
By using the formula of square difference of two numbers, (a ^ 2-9) is decomposed into two factors: (a + 3) (a-b)

Extract the common factor. What do you mean?

Extracting the common factor is to extract the same factor in each term, and the rest will continue to be calculated according to the original
For example, AB + BC = b * (a + C)
And 3 * 4 + 4 * 5 + 4 * 6 = 4 * (3 + 5 + 6)
And so on. Mainly for the convenience of calculation

If each term of a polynomial has a common factor, then the common factor must be ()
A. Number B. monomial C. polynomial D. integral

The letters in terms of polynomials can be either single numbers or letters or polynomials, but they are all integers. Therefore, the common factor must be integers. So D