求下列对数形式写成指数形式(1)log1/5^25=-2(2)log3^81=4

Question

如题所述

Answer 1

log<1/5> 25
=log<5> 25/log<5>(1/5)
= 2/(-1)
=-2
---------------
log<3>81
=log<3> 3^4
=4追问

看不太懂

追答

换底
logb = logb/loga
log 25
=log 25 / log 1/5
=log 5^2 / log 5^(-1)
=2/(-1)
=-2

本回答被提问者采纳