Bài 1: So sánh
a) Ta có: \(9^{1005}=\left(3^2\right)^{1005}\)
\(=3^{2010}>3^{2009}\)
hay \(3^{2009}< 9^{1005}\)
b) Ta có: \(2^{75}=2^{3\cdot25}=\left(2^3\right)^{25}=8^{25}\)
\(3^{50}=3^{2\cdot25}=\left(3^2\right)^{25}=9^{25}\)
Vì \(8^{25}< 9^{25}\) nên \(2^{75}< 3^{50}\)
c) Ta có: \(99^{20}=99^{2\cdot10}=\left(99^2\right)^{10}=9801^{10}\)
Vì \(9801^{10}< 9999^{10}\) nên \(99^{20}< 9999^{10}\)