先化简再求值:y(x+y)+(x-y)2-x2-2y2,其中x=-1/3,y=3.

问题描述:

先化简再求值:y(x+y)+(x-y)2-x2-2y2,其中x=-

1
3
,y=3.

y(x+y)+(x-y)2-x2-2y2
=xy+y2+x2-2xy+y2-x2-2y2
=-xy
=-(-

1
3
)×3
=1