ĐÁP ÁN C. ( ) ( ) ( )2 2P X Y Y X X Y Y X XY X Y= + = + = +( )...
Câu 28. Đáp án C.
( ) ( ) ( )
2
2
P x y y x x y y x xy x y= + = + = +( ) ( ) ( )( )
3
3
= + = + = + - +Q x x y y x y x y x xy y = - = - = - +R x y x y x y x yVậy R =