RIOPLATENSE 1995 Problem 2

In a circle of center $O$ and radius $r$ , a triangle $ABC$ of orthocenter $H$ is inscribed. It is considered a triangle $A'B'C'$ whose sides have by length the measurements of the segments $AB, CH$ and $2r$ . Determine the triangle $ABC$ so that the area of the triangle $A'B'C'$ is maximum.