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=-
,y=3. 1 3
答
y(x+y)+(x-y)2-x2-2y2
=xy+y2+x2-2xy+y2-x2-2y2
=-xy
=-(-
)×31 3
=1