... = 2 2 2 ( ) ( ) a b c b c a A Bb c c a a b b c c a a b+ + + + + = ++ + + + + + 0 ,25 [ ]331 1 1 13 ( ) ( ) ( ) 2 1 1 1 1 93 ( )( )( )3 2 23 2 A a b b c c a a b b c c a a b b c c a a ... c a A + = + + + + + + + + + + + + + =+ + + 0 ,25 2 2 2 2 2 1 ( ) ( )( )11 .2 2 a b c a b c a b b c c a a b b c c a B B= + + + + + + + + ++ + + 0 ,25 Từ đó tacó VT3 1 2 2 2 VP ... xảy ra khi a= b=c=1/30 ,25 V .a 2 1 1Ta có: AB = 2 , trung điểm M ( 5 5; 2 2), pt (AB): x y 5 = 0 0 ,25 SABC= 1 2 d(C, AB).AB = 3 2 d(C, AB)= 3 2 Gọi G(t;3t-8) là trọng tâm tam...