A=\(\frac{1}{2}.\frac{3}{4}.\frac{5}{6}.....\frac{2499}{2500}\)
B=\(\frac{2}{3}.\frac{4}{5}.\frac{6}{7}....\frac{2500}{2501}\)
A.B=\(\frac{1.2.3.4.5....2499.2500}{2.3.4.5.6......2499.2500.2501}=\frac{1}{2501}\)
so sanh A.A va A.B
ta cm duoc \(\frac{1}{2}