A (real) polynomial of degree $d$ has at most $d$ (real) roots
The catch is the only things I can cite are
1) The Division Algorithm for Polynomials
2) Prop 6.19: Let p(x) be a real polynomial. The number z is a root of p(x) iff there exists polynomial q(x) such that p(x)=(x-z)q(x).
Any help appreciated.