Đặt M = \(1+9+9^2+......+9^{2010}\)
\(9M=9+9^2+9^3+......+9^{2011}\)
\(9M-M=8M=9^{2011}-1\)
Đặt K = \(1+9+9^2+......+9^{2009}\)
\(9K=9+9^2+9^3+.....+9^{2010}\)
\(9K-K=8K=9^{2010}-1\)
\(\Rightarrow A=\frac{9^{2011}-1}{9^{2010}-1}\)
Đặt H=\(1+5+5^2+....+5^{2010}\)
\(5H=5+5^2+......+5^{2011}\)
\(5H-H=4H=5^{2011}-1\)
ĐẶT G = \(1+5+5^2+.......+5^{2009}\)
\(5G-G=4G=5^{2010}-1\)
\(\Rightarrow B=\frac{5^{2011}-1}{5^{2010}-1}\)
Rồi bạn so sánh sẽ ra ngay