Question

設x,y,z＞0,且xyz(x+y+z)=1,則(x+y)(y+z)的最小值是(    )

A.1           B.2                C.4           D.不存在

Answer 1

解析:∵(x+y)(y+z)=xy+y²+xz+yz,而(x+y+z)·y=,

即xy+y²+yz=,

因此xy+y²+yz+xz=+xz≥2,

即(x+y)(y+z)≥2.選B.

答案:B