问题
解答题
解答题: (1)x(y-1)-y(x-1) (2)(x-3y)(x+3y)-(x-3y)2 (3)
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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=
x-2x+1 2
y2-2 3
x+3 2
y2=-3x+y2,1 3
把x=-1,y=
代入上式,得1 2
上式=-3×(-1)+(
)21 2
=3+1 4
=
.13 4