问题
选择题
如果(x-y)2+M=x2+xy+y2,则M等于( )
A.3xy
B.2xy
C.xy
D.0
答案
由题意得M=(x2+xy+y2)-(x-y)2=x2+xy+y2-x2+2xy-y2=3xy.
故选A.
如果(x-y)2+M=x2+xy+y2,则M等于( )
A.3xy
B.2xy
C.xy
D.0
由题意得M=(x2+xy+y2)-(x-y)2=x2+xy+y2-x2+2xy-y2=3xy.
故选A.