MathDB
Putnam 1991 A3 and follow-up

Source: Curiosity

October 20, 2008
Putnamalgebrapolynomialcollege contests

Problem Statement

Find all real polynomials p(x) p(x) of degree n2 n \ge 2 for which there exist real numbers r1<r2<...<rn r_1 < r_2 < ... < r_n such that (i) p(r_i) \equal{} 0, 1 \le i \le n, and (ii) p' \left( \frac {r_i \plus{} r_{i \plus{} 1}}{2} \right) \equal{} 0, 1 \le i \le n \minus{} 1. Follow-up: In terms of n n, what is the maximum value of k k for which k k consecutive real roots of a polynomial p(x) p(x) of degree n n can have this property? (By "consecutive" I mean we order the real roots of p(x) p(x) and ignore the complex roots.) In particular, is k \equal{} n \minus{} 1 possible for n3 n \ge 3?