area of triangle with lattice points inside triangle and on the sides
Source: 1967 Swedish Mathematical Competition p6
March 21, 2021
geometrylatticecombinatorial geometrytriangle area
Problem Statement
The vertices of a triangle are lattice points. There are no lattice points on the sides (apart from the vertices) and lattice points inside the triangle. Show that its area is . Find the formula for the general case where there are also lattice points on the sides (apart from the vertices).