Ta có: $log7.log13\leq (\frac{log7+log13}{2})^2=(\frac{log91}{2})^2<(\frac{log100}{2})^2=1$Từ đó suy ra $\frac{1}{log7}>\frac{log13}{log11}$
Ta có: $log7.log13\leq (\frac{log7+log13}{2})^2=(\frac{log91}{2})^2<(\frac{100}{2})^2=1<log11$Từ đó suy ra $\frac{1}{log7}>\frac{log13}{log11}$
Ta có: $log7.log13\leq (\frac{log7+log13}{2})^2=(\frac{log91}{2})^2<(\frac{
log100}{2})^2=1$Từ đó suy ra $\frac{1}{log7}>\frac{log13}{log11}$