... MF2 ≤ +3 22 Váûy MF2 - ảt GTNN l 3 22 =khi x -3 +GTLN l 3 22 =khi x 3M1( ,- )x yM2 (- , )x yM3 (- ,- )x y HS kiãøm tra ta âäü ca M1 , M2 , M3 ... = a2 - c2 = 1 ( ):Váûy PTCT ca E2 2x y19 1+ = . :b Theo CT2cxMF aa= − -våïi a ≤ x ≤ a Váûy2ca caa MF aa a− ≤ ≤ +⇔ -3 22 ≤ MF2 ≤ +3 22 Váûy MF2 - ảt GTNN ... +) => MF12 - MF22 = ( )4cx 1 Do M ∈ ( )E nãn MF1 + MF2 = ( )2a 2 ( )( ) => (1 2 MF1 + MF2)(MF1 - MF2 ) = 4cx⇔ (2a MF1 - MF2 ) = 4cx⇔ MF1 - MF2 =2cxa (...