已知y=1/3x-1,那么1/3x2-2xy+3y2-2的值是_.

问题描述:

已知y=

1
3
x-1,那么
1
3
x2-2xy+3y2-2的值是______.

∵y=

1
3
x-1,∴
1
3
x2-2xy+3y2-2=
1
3
(x2-6xy+9y2)-2=
1
3
(x-3y)2-2=
1
3
×9-2=1.