3 3 9 3 6 34 4 4 4 4 2 VẬY X2 Y2 Z2 31 Y 1 Z 1 X 2 + + ≥+ + ++ + +

3 .3 3 9 3 6 3

4 4 4 4 4 2

Vậy x

2

y

2

z

2

3

1 y 1 z 1 x 2 + + ≥

+ + +