... 20 11 20 12 20 12 20 12 20 12 S C C C C C C = + + + + + + + L L 0 ,25 ( ) ( ) 20 11 20 12 20 11 20 12 20 12 20 12 1 1 1 1 20 12 2 2 1007 2 S = + + + = × + = × 0 ,25 Vậy 20 12 1007 2 S = × 0 ,25 Câu VI B ... ) 1 20 12 20 12 20 12 20 12 2011 20 12 20 12! 1 20 12 ! 20 12 ! k k k k k k k C kC C k C C C k k - + = + = + = + - với 0,1 ,2, ,20 12 k " = 0 ,25 ( ) ( ) 0 1 20 11 0 1 20 12 20 11 20 11 20 11 ... Z0 ,25 2. (1 ,25 im)Hphngtrỡnh ( ) ( ) 2 23 2 8 12 * 2 12 0 **x yx xy y + = ỡ ù ớ + + = ù ợTh(*)vo(**)tac: ( )3 2 2 2 2 8 0x xy x y y + + + =0 ,25 ( ) ( )( )3 3 2 28 2 0 2 2 4...