Question

若x,y是正數，則（x+）²+(y+)²的最小值是(    )

A.3             B.             C.4             D.

Answer 1

解析:（x+）²+(y+)²=(x²+)+(y²+)+(+)≥2+2+2=4,

當且僅當即x=y=取等號.

答案:C