已知x+y=2,则12x2+xy+12y2等于(  ) A.2 B.4 C.12 D.-2

问题描述:

已知x+y=2,则

1
2
x2+xy+
1
2
y2等于(  )
A. 2
B. 4
C.
1
2

D. -2

∵x+y=2,

1
2
x2+xy+
1
2
y2=
1
2
(x2+2xy+y2)=
1
2
(x+y)2=
1
2
×22=2.
故选A.