GCD of the coefficients of a polynomial

The content of a polynomial is the GCD (greatest common divisor) of its coefficients. The content command computes the content of a polynomial.

content takes P, a polynomial given by a symbolic expression or by the list of its coefficients.
content(P) returns the content of P.

content(6*x^2-3*x+9)

or:

content([6,-3,9],x))