Algebraic geometry on imaginary triangles

Abstract

We extend the notion of triangle to imaginary triangles with complex valued sides and angles, and parametrize families of such triangles by plane algebraic curves. We study in detail families of triangles with two commensurable angles, and apply the theory of plane Cremona transformations to find "Pythagorean theorems" for these triangles, which are interpreted as the implicit equations of their parametrizing curves.