Resultants and discriminants of multiplication polynomials for elliptic curves

In this article, we prove that the resultant of the standard multiplication polynomials AnAn, BnBn of an elliptic curve in the form y2=x3+ax+by2=x3+ax+b is (16Δ)n2(n2−1)6, where Δ=−(4a3+27b2)Δ=−(4a3+27b2) is the discriminant of the curve. We give an application to good reduction of an associated Lattès map. We also prove a similar result for the discriminant of the largest squarefree factor of BnBn.