how to declare variable as constant without defining its value

suppose u have two polynomial equations - (a*x^3+b*x^2+c*x+d , a*x^2+b*x+c) and u want to find common roots for the two equations . here u need to find roots in form of a , b , c ,d

CODE

syms x

gcd(a*x^3+b*x^2+c*x+d , a*x^2+b*x+c)

Answer 1

[Matt J]

It seems clear that they will only ever have common roots if d=0, in which case the common roots will be,

syms x a b c
solve(a*x^2+b*x+c==0)

ans =