有理数指数幂 设a,b,c均为不等于1的正数,x,y,z都是有理数,且a^x=b^y=c^z,1/x+1/y+1/z=0,求abc的值
问题描述：
有理数指数幂 设a,b,c均为不等于1的正数,x,y,z都是有理数,且a^x=b^y=c^z,1/x+1/y+1/z=0,求abc的值
答
a^x=b^y=c^z,
两边取lg， 得：xlga=ylgb=zlgc ==> y/x=lga/lgb;y/z=lgc/lgb
1/x+1/y+1/z=0,
两边乘以y，得：y/x+1+y/z=0
==> lga/lgb+lgb/lgb+lgc/lgb=0
==> （lga+lgb+lgc)/lgb=0
==>lgabc=0
==>abc=1
ok
答
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