  We present a Poisson formula for sparse resultants and a formula for the
product of the roots of a family of Laurent polynomials, which are valid for
arbitrary families of supports. To obtain these formulae, we show that the
sparse resultant associated to a family of supports can be identified with the
resultant of a suitable multiprojective toric cycle in the sense of Remond.
This connection allows to study sparse resultants using multiprojective
elimination theory and intersection theory of toric varieties.
