Show that for any positive integer n there is an integer N such that the product x1x2⋯xn can be expressed identically in the form
x1x2⋯xn=i=1∑Nci(ai1x1+ai2x2+⋯+ainxn)n
where the ci are rational numbers and each aij is one of the numbers, −1,0,1. Putnamalgebrapolynomialcollege contests