Let ABC be an acute triangle and let k1,k2,k3 be the circles with diameters BC,CA,AB, respectively. Let K be the radical center of these circles. Segments AK,CK,BK meet k1,k2,k3 again at D,E,F, respectively. If the areas of triangles ABC,DBC,ECA,FAB are u,x,y,z, respectively, prove that u2=x2+y2+z2. geometrytrigonometrygeometric transformationreflectioncircumcircleradical axisgeometry unsolved