OA²+BC²=OB²+CA²→OA²-OB²=CA²-BC²→(OA-OB)·(OA+OB)=(CA-BC)·(CA+BC)→
BA·(OA+OB)=BA·(CA-BC)→BA·(OA+OB-CA+BC)=0→BA·(2*OC)=0