Obtener punto 3 de un triángulo equilátero desde los otros 2

procedure CreateEquilateralTriangle(x1, y1, x2, y2: Double; var x3, y3: Double);
const
Sin60 = 0.86602540378443864676372317075294;
const
Cos60 = 0.50000000000000000000000000000000;
begin
{ Translate for x1,y1 to be origin }
x2 := x2 - x1;
y2 := y2 - y1;
{ Rotate 60 degrees and translate back }
x3 := ((x2 * Cos60) - (y2 * Sin60)) + x1;
y3 := ((y2 * Cos60) + (x2 * Sin60)) + y1;
end;
(* End Of Create Equilateral Triangle *)

Autor: Arash Partow
Homepage: http://www.partow.net