设a^x=b^y=c^z=k
得loga k =x
logb k =y
logc k =z
1/x=1/loga k=logk a
1/y=logk b
1/z=logk c
so:1/x+1/y+1/z=0
logk a+logk b+logk c=0
logk abc=0
abc=1