Given any two polynomials in a single variable it is always possible to eliminate the variable and obtain a formula showing the relationship between the two polynomials.

Let $p(x) = x^2 + 2x$ and $q(x) = x^2 + x + 1$ then, using a method which does not depend on knowing the answer, show that the relationship between the polynomials is:

$p^2 - 2pq + q^2 + 3p - 4q + 3 = 0$