问题 解答题
解答题:
(1)x(y-1)-y(x-1)
(2)(x-3y)(x+3y)-(x-3y)2
(3)
1
2
x-2(x-
1
3
y2)+(-
3
2
x+
1
3
y2),其中x=-1,y=
1
2
答案

(1)原式=xy-x-xy+y=-x+y;

(2)原式=x2-(3y)2-x2+6xy+(3y)2=6xy-18y2

(3)原式=

1
2
x-2x+
2
3
y2-
3
2
x+
1
3
y2=-3x+y2

把x=-1,y=

1
2
代入上式,得

上式=-3×(-1)+(

1
2
)2

=3+

1
4

=

13
4

单项选择题
单项选择题