... Vi-ét , ta có : 1 2 1 2 12 .x xx x m+ ==. ( ) 2 2 2 1 2 1 2 1 2 1 2 1 2 1 2 1 16 2. . 6.x xx x x x x xx xx x + + = − + ⇔ + − = − 2 2 24 8 12 0 16 2 6 2 0 ... cầu bài toán ( ) ( ) 1 1 2 2 2 2, , 2 2x y x yd A d B+ + + +∆ = ∆ ⇔ = ( ) ( ) 2 2 1 2 1 2 3 2 2 3 2 2 3 2 2 3 2 2x m x m x m x m⇔ + + = + + ⇔ + + = + + ( ) ( ) 2 2 1 2 3 2 2 3 2 2 0x ... thẳng AB có hệ số góc ( )( )3 3 2 2 2 2 1 2 1 2 1 2 1 2 1 2 1 3ABx x x x m x xy ykx x x x− − − + −−= =− − ( ) ( ) 2 2 1 2 1 2 1 2 3ABk x x x x x x m= + − − + + 2 2 2 2 64 63...