Question

求

1

2

x2-2xy+

1

3

减去-

2

3

x2+xy-

2

3

的差．

Answer 1

1

2

x²-2xy+

1

3

-（-

2

3

x²+xy-

2

3

）=

1

2

x²-2xy+

1

3

+

2

3

x²-xy+

2

3

=

7

6

x²-3xy+1．