Question

设m=x²+y²-2x+2y,n=-5,得m、n的大小关系是(    )

A.m＞n                                B.m＜n

C.m=n                                 D.与x、y的取值有关

Answer 1

解析：（作差法）m-n=x²+y²-2x+2y-(-5)

=x²+y²-2x+2y+5=x²-2x+1+y²+2y+1+3

=(x-1)²+(y+1)²+3＞0.

∴m＞n.

答案：A