\(A=\dfrac{2}{1}\cdot\dfrac{2}{3}\cdot\dfrac{3}{2}\cdot\dfrac{3}{4}\cdot...\cdot\dfrac{20}{19}\cdot\dfrac{20}{21}\)
\(=\dfrac{2}{1}\cdot\dfrac{3}{2}\cdot...\cdot\dfrac{20}{19}\cdot\dfrac{2}{3}\cdot\dfrac{3}{4}\cdot...\cdot\dfrac{20}{21}\)
=20/1*2/21=40/21
\(Q=1+\dfrac{1}{2}-\dfrac{1}{2}-\dfrac{1}{3}+....-\dfrac{1}{1010}-\dfrac{1}{1011}\)
=1-1/1011=1010/1011
A>1
Q<1
=>A>Q