Dễ thấy B < 1 vì 102011 + 1 < 102012 + 1. Áp dụng tính chất nếu \(\frac{a}{b}<1\) thì \(\frac{a}{b}<\frac{a+m}{b+m}\) ta có :
\(B=\frac{10^{2011}+1}{10^{2012}+1}<\frac{\left(10^{2011}+1\right)+9}{\left(10^{2012}+1\right)+9}=\frac{10^{2011}+10}{10^{2012}+10}=\frac{10.\left(10^{2010}+1\right)}{10.\left(10^{2011}+1\right)}=\frac{10^{2010}+1}{10^{2011}+1}=A\)
Vậy A > B