答案
解:(6x
2+4xy)-2(3x
2+xy-
y
2)
=6x
2+4xy-6x
2-2xy+y
2=[6x
2+(-6x
2)]+[4xy+(-2xy)]+y
2=0+2xy+y
2=2xy+y
2,
把x=2,y=-3代入上式得:原式=2×2×(-3)+(-3)
2=-12+9=-3.
解:(6x
2+4xy)-2(3x
2+xy-
y
2)
=6x
2+4xy-6x
2-2xy+y
2=[6x
2+(-6x
2)]+[4xy+(-2xy)]+y
2=0+2xy+y
2=2xy+y
2,
把x=2,y=-3代入上式得:原式=2×2×(-3)+(-3)
2=-12+9=-3.