June 23–July 6, 2009

Problem

Find all the integer solutions to the system of equations

ab + cd = -1, ac + bd = -1, ad + bc = -1

Solution

here. (Most people had variations on this; some more elegant.)

List of solvers

Trey Sakazaki (middle school), Tuan Le (high school), Matt Inouye, Huy Hoang-Nguyen (UW undergrad), Jizhou Li (undergrad, U. Michigan), Tran Thanh Nam (Tomsk Polytechnic University, Russia.), Chaitanya Rachabattuni (undergrad, U. Minnesota), Mauricio Duarte (UW graduate), Gary Raymond (staff), Mike Goodman, Mukund Tirumalai, Steve Wilmarth, Lloyd Sakazaki, Yo Tu, Lincoln Atkinson (outside).

Chaitanya Rachabattuni wins the prize!