1/x+1/y=1/6 1/y+1/z=1/9 1/z+1/x=1/15 求xyz/xy+yz+xz的值

1/x+1/y=1/6 1/y+1/z=1/9 1/z+1/x=1/15 2(1/x+1/y+1/z)=1/6+1/9+1/15=31/901/x+1/y+1/z=31/180(xy+yz+zx)/xyz=1/z+1/x+1/y=31/180xyz/(xy+yz+xz)=180/31