... 3 3 32 2 21 ( )2 2 2 3a b ca b ca b b c c a+ + ≥ + ++ + +f/3 3 32 2 21 ( )4 ( ) ( ) ( )a b ca b cb c c a a b+ + ≥ + ++ + +g/ 3 3 31 ( ) ( )( ) ( )( ) ( )( ) 4a b ca b ... 01 2 1 2 ( , , , ) ( , , , )Max ( , , , ) : ( , , , )n nDn nf x x x M x x x Df Mx x x D f x x x M = =1 2 1 20 0 0 0 0 01 2 1 2 ( , , , ) ( , , , )Min ( , , , ) : ( , , , ... < 25. 1 21yx x= +− ( Viết ( )2 11 2 1 1 231 1 1x xx x x xx x x x x x− +− + −+ = + = + +− − −) 26.4 91yx x= +−: ( Viết ( ) ( ) ( )4 1 9 1 4 14 9 94 91 1 1x...