... phai tim (a) qua true tung nen (a) c6 phacmg trinh dang BA = ( -2; 2; 3), BC = (2- 2; 9), BA,BC = (-9; -5; 10) 3 -2 -2 2 9 2 = ( 12; 24 ; -8) Ax + Cz = (A^ + C^^ 0) V i A ( l ; 4; -3) € a nen A - ... AD = (2; 2; 2) DiAB; = AC; -2 2 +6 C,(a; 0; Hinh 95 AD) a^l), c M A,(0;0;aV2), -2 2 +3 2 B' A' 1- M(0;0;^), B • = 3.10-6.6 + M ) = -18 f 74 a) ABCD.A'B'CD' la hinh hop nen: AB = DC, DC ' 2 Toa ... 10 20 20 X-^'- -V- Cdnh 2: Bien ddi ve phai: = - - b+a — DA ^ — DB ^ — DC 10 20 20 = - — b + a + -{c2 + M^)+ —(Z)M+ MB)+—-{DM = (DM 10 20 + MC) 20 _L DM + — DM +— Z)M +— M4 +— MB +— MC 10 20 20 ...