已知3^a=2，那么log以3为底8－2log以3为底6用表示为

Question

如题所述

Answer 1

3^a=2

所以
log(3,2)=a -----就这样表示对数吧
所以
log以3为底8－2log以3为底6

=log(3,2³)-2（log(3,2)+1）
=3log(3,2)-2log(3,2)-2
=log(3,2)-2
=a-2追问

=log(3,2³)-2（log(3,2)+1）这＋1怎么得来

追答

log以3为底6=log(3,6)=log(3,2×3)=log(3,2)+log(3,3)=log(3,2)+1

Answer 2

3^a=2
log3(2)=a

log3(8) - 2log3(6)
= log3(2³) - 2log3(3*2)
= 3log3(2) - 2log3(3) - 2log3(2)
= log3(2) - 2
= a - 2追问

这里 3log3(2) - 2log3(3) - 2log3(2)怎么求出
= log3(2) - 2

追答

3log3(2) - 2log3(3) - 2log3(2)
= {3log3(2) - 2log3(2)} - 2log3(3)
= (3-2)log3(2) - 2*1
= log3(2) - 2