∵xy/(x+y)=1∴(x+y)/(xy)=1/1∴1/x+1/y=1.(1)∵yz/(y+z)=2∴(y+z)/(yz)=1/2∴1/y+1/z=1/2.(2)∵zx/(z+x)=3∴(z+x)/(zx)=1/3∴1/z+1/x=1/3.(3)(1)+(3)-(2)得：1/x+1/x=1+1/3-1/22/x=5/6x=12/5