879bfcb2-a2b1-48b4-996c-046525e0133e

879bfcb2-a2b1-48b4-996c-046525e0133e,a b ab b c bc,a2 b2 c2 ab bc ac,已知a b 4 ab c 2 4 0,ab分之a b bc分之b c,已知ab分之x bc分之y,bc a ac b ab c,a 2 b 2 c 2 ab bc ca,设a b c 0 则2a21 ab,a b c a b c ab