Two circles with different radii intersect in two points A and B. Let the common tangents of the two circles be MN and ST such that M,S lie on the first circle, and N,T on the second. Prove that the orthocenters of the triangles AMN, AST, BMN and BST are the four vertices of a rectangle. geometryrectanglegeometric transformationhomothetyreflectioncircumcircleparallelogram