Vì 1320+1/1319+1>1
=>1320+1/1319+1>1320+1+12/1319+1+12
Ta có: 1320+1+12/1319+12
= 1320+13/1319+13
=13(1319+1)/13(1318+1)
= 1319+1/1318+1
=> 1320+1/1319+1> 1319+1/1318+1
Vậy A<B
\(B=\frac{13^{20}+1}{13^{19}+1}>1\)
\(B=\frac{13^{20}+1}{13^{19}+1}>\frac{13^{20}+1+12}{13^{19}+1+12}\)
\(B=\frac{13^{20}+13}{13^{19}+13}=\frac{13\left(13^{19}+1\right)}{13\left(13^{18}+1\right)}\)
\(B=\frac{13^{19}+1}{13^{18}+1}=A\)
\(\Rightarrow B>A\)
Tất cả đọc kĩ lại đi. Đừng có xem qua loa rồi nói tôi như vậy.