log27 $log-27 5$ =$\frac{1}{3}$$log_3 5=a suy ra $log_3 5$ =3alog27 = $\frac{1}{3}$ $log_3 5 $ =a $\Rightarrow$ $log_3 5$ =3a log27 của 5 =13log35 =a suy ra log35 = 3a
log87 =13 log27 =b ⇒ log27 = 3b
log23=c
log635 = log235log26=log25+log27log22+log23= log35log32+log271+log23
=3ac+3b1+c