化简求值:[(x+2y)2-(x+y)(3x-y)-5y2]÷2x,其中x=-2,y=1/2.

问题描述:

化简求值:[(x+2y)2-(x+y)(3x-y)-5y2]÷2x,其中x=-2,y=

1
2

[(x+2y)2-(x+y)(3x-y)-5y2]÷2x
=(x2+4xy+4y2-3x2-2xy+y2-5y2)÷2x
=(-2x2+2xy)÷2x
=y-x,
当x=-2,y=

1
2
时,
原式=
1
2
-(-2)=
5
2