若A=4x2-4xy+y2,B=2/3x2-4/3xy-y2.求A-3B的值.

问题描述:

若A=4x2-4xy+y2,B=

2
3
x2-
4
3
xy-y2.求A-3B的值.

∵A=4x2-4xy+y2,B=

2
3
x2-
4
3
xy-y2
∴A-3B=(4x2-4xy+y2)-3(
2
3
x2-
4
3
xy-y2
=4x2-4xy+y2-2x2+4xy+3y2
=2x2+4y2