x,y,z均为正数,xy+yz+zx=1,求x+y+z的最小值设M=2(x+y+z)²　　则M=2x²+2y²+2z²+4xy+4yz+4zx=(x²+y²)+(y²+z²)+(z²+x²)+4(xy+yz+zx)≥2xy+2yz+2zx+4=6因此,当x=y=z...