trapezoids with interior angles of 90^o, 90^o, 45^o,135^o
Source: 2001 Estonia National Olympiad Final Round grade 11 p5
March 12, 2020
trapezoidcombinatorial geometrycombinatoricslattice
Problem Statement
Consider all trapezoids in a coordinate plane with interior angles of and whose bases are parallel to a coordinate axis and whose vertices have integer coordinates. Define the size of such a trapezoid as the total number of points with integer coordinates inside and on the boundary of the trapezoid.
(a) How many pairwise non-congruent such trapezoids of size are there?
(b) Find all positive integers not greater than that do not appear as sizes of any such trapezoid.