... C tự C ( 4; - 4) , loi gúc BA ( ) C ( 6 ;2) , tha Vi b = ịị B 2; 2 - t gt cú ( x - 1) ( y - 1) ị - Do ú 0 .25 x + y - xy ị xy 1 + - x y ổ1 1 1 ữ + + 2 - ỗ + + ữ ữ ữ ỗ xy yz zx ốx y z ứ ổ ữ 1 P ... vtpt l A D = - 3;1 cú phng trỡnh - ( x - 3) + y - = 3x - y - = ( ) Gi ta im B b; 3b - ta cú ộb = 2 A B = 10 ị ( b - 3) + ( 3b - 9) = 10 ờb = ( Vi b = ịị B 4; ) ã C tự C ( 4; - 4) , loi gúc ... AC AE - AD uuuur uuur A C A D ã E - A C A D cosCA ã D =0 = A B A E cos BA ị A I ^ DE ( b )( ) 0 .25 Phng trỡnh ng thng A I : ( x - 4) + y - = 3x + y - 14 = ùỡù 3x + y - 14 = ùù 2x - y - = ợ...