计算：3的a次方=2 则log3 8-2log3 6等于麻烦写下步骤 好让我预习

3^a=2 即 log3 2=a
log3 8-2log3 6
=log3 2^3-2log3 2*3
=3log3 2-2(log3 2+log3 3)
=3a-2(a+1)
=3a-2a-2
=a-2

log3 8=3log3 2
2lo3 6=2(log3 3+log3 2)=2+2log3 2
所以 原式=2+5log3 2=2+5a

由于：3^a=2
则：a=log3(2)
则：
log3(8)-2log3(6)
=log3(2^3)-2log3(2*3)
=3log3(2)-2[log3(2)+log3(3)]
=3a-2[a+1]
=a-2