Problem

Source: IMO LongList 1959-1966 Problem 28

Tags: geometry, circle, Locus, Locus problems, IMO Longlist, IMO Shortlist



In the plane, consider a circle with center $S$ and radius $1.$ Let $ABC$ be an arbitrary triangle having this circle as its incircle, and assume that $SA\leq SB\leq SC.$ Find the locus of a.) all vertices $A$ of such triangles; b.) all vertices $B$ of such triangles; c.) all vertices $C$ of such triangles.