MathDB
CHMMC 2021-21 Proof 3

Source:

September 1, 2022
algebra

Problem Statement

Let F(x1,...,xn)F(x_1,..., x_n) be a polynomial with real coefficients in n>1 n > 1 “indeterminate” variables x1,...,xnx_1,..., x_n. We say that FF is nn-alternating if for all integers 1i<jn1 \le i < j \le n, F(x1,...,xi,...,xj,...,xn)=F(x1,...,xj,...,xi,...,xn),F(x_1,..., x_i,..., x_j,..., x_n) = - F(x_1,..., x_j,..., x_i,..., x_n), i.e. swapping the order of indeterminates xi,xjx_i, x_j flips the sign of the polynomial. For example, x12x2x22x1x^2_1x_2 - x^2_2x_1 is 22-alternating, whereas x1x2x3+2x2x3x_1x_2x_3 +2x_2x_3 is not 33-alternating.
Note: two polynomials P(x1,...,xn)P(x_1,..., x_n) and Q(x1,...,xn)Q(x_1,..., x_n) are considered equal if and only if each monomial constituent ax1k1...xnknax^{k_1}_1... x^{k_n}_n of PP appears in QQ with the same coefficient aa, and vice versa. This is equivalent to saying that P(x1,...,xn)=0P(x_1,..., x_n) = 0 if and only if every possible monomial constituent of PP has coefficient 00.
(1) Compute a 33-alternating polynomial of degree 33. (2) Prove that the degree of any nonzero nn-alternating polynomial is at least (n2){n \choose 2}.