A=20^10+1/20^10-1
A=20^10-1+2/20^10-1
A=20^10-1/20^10-1+2/20^10-1
A=1+2/20^10-1
B=20^10-1/20^10-3
B=20^10-3+2/20^10-3
B=20^10-3/20^10-3+2/20^10-3
B=1+2/20^10-3
Vì 20^10-1>20^10-3 nên 2/20^10-1<2/20^10-3
=>A<B
Ta có: \(20^{10}-1>20^{10}-3\)
\(\Rightarrow\frac{20^{10}-1}{20^{10}-3}>1\)
\(\Rightarrow\frac{20^{10}-1}{20^{10}-3}>\frac{20^{10}-1+2}{20^{10}-3+2}=\frac{20^{10}+1}{20^{10}-1}=B\)
Vậy \(A>B\)