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=
x2-2 3
xy-y2.求A-3B的值. 4 3
答
∵A=4x2-4xy+y2,B=
x2-2 3
xy-y2,4 3
∴A-3B=(4x2-4xy+y2)-3(
x2-2 3
xy-y2)4 3
=4x2-4xy+y2-2x2+4xy+3y2
=2x2+4y2.