已知log9[log8(log7x)]=0,则x=
问题描述：
已知log9[log8(log7x)]=0,则x=
还有一题呃:lga+lgb=2lg(a-2b),求log4(a/b)
答
log8(log7x)=1
log7(x)=8
x=7^8
lga+lgb=lg(ab)=2lg(a-2b)=lg(a-2b)^2
(a-2b)^2=ab
a^2-5ab+4b^2=(a-b)(a-4b)=0
a-2b>0,a>0,b>0
a-b>b>0
a-4b=0,a=4b
log4(a/b)=log4(4)=1