 2 2 2X Y Y X X2 2 4 1 1    

1)

 

2

2

2

x y y x x2 2 4 1 1    HD: hệ ^2y



^{1 4y}

²

^1



^1_x^^1 _x¹

²

^1 Xét ^{f t}

 

^t



^{1 t}

²

^1



^{ f t}

^{ }

^{đồng biến2y 1}_x ^

^

^{x y;}

^

^{ }_^1;1₂^_        x x x y y2 1 2 4 4 4 3 2 9 3 0.