Let k, ℓ and m be positive integers. Let ABCDEF be a hexagon that has a center of symmetry whose angles are all 120∘ and let its sidelengths be AB=k, BC=ℓ and CD=m. Let f(k,ℓ,m) denote the number of ways we can partition hexagon ABCDEF into rhombi with unit sides and an angle of 120∘.
Prove that by fixing ℓ and m, there exists polynomial gℓ,m such that f(k,ℓ,m)=gℓ,m(k) for every positive integer k, and find the degree of gℓ,m in terms of ℓ and m.
Submitted by Zoltán Gyenes, Budapest combinatoricscountingcombinatorial geometryalgebrapolynomial