1.
令a^x=b^y=c^z=t,由a,b,c均为正得t>0
x=loga(t) 1/x=logt(a)
同理,1/y=logt(b) 1/z=logt(c)
1/x+1/y+1/z=0
logt(a)+logt(b)+logt(c)=0
logt(abc)=0
abc=1