答案
解:(1)2(x
2y+xy)-3(x
2y-xy)-4x
2y
=2x
2y+2xy-3x
2y+3xy-4x
2y
=-5x
2y+5xy,
当x=1,y=-1时,原式=-5×1×(-1)+5×1×(-1)=0;
(2)
2x3+4x-x2-(x+3x2-2x3)=4x
3+4x-
x
2-x-3x
2+2x
3
=4x
3-
x
2+3x,
当x=-3时,原式=4×(-27)-30-9=-147;
(3)
a2b-5ac-(3a2c-a2b)+(3ac-4a2c)=
a
2b-5ac-3a
2c+a
2b+3ac-4a
2c
=
a
2b-2ac-7a
2c,
当a=-1,b=2,c=-2时,原式=
×1×2-2×(-1)×(-2)-7×1×(-2)=13.
解:(1)2(x
2y+xy)-3(x
2y-xy)-4x
2y
=2x
2y+2xy-3x
2y+3xy-4x
2y
=-5x
2y+5xy,
当x=1,y=-1时,原式=-5×1×(-1)+5×1×(-1)=0;
(2)
2x3+4x-x2-(x+3x2-2x3)=4x
3+4x-
x
2-x-3x
2+2x
3
=4x
3-
x
2+3x,
当x=-3时,原式=4×(-27)-30-9=-147;
(3)
a2b-5ac-(3a2c-a2b)+(3ac-4a2c)=
a
2b-5ac-3a
2c+a
2b+3ac-4a
2c
=
a
2b-2ac-7a
2c,
当a=-1,b=2,c=-2时,原式=
×1×2-2×(-1)×(-2)-7×1×(-2)=13.