\(2^{91}=\left(2^{13}\right)^7=73728^7\)
\(5^{35}=\left(5^5\right)^7=3125^7\) nhỏ hơn \(73728^7\)
\(\Rightarrow2^{91}\) lớn hơn \(5^{35}\)
\(b,3^{400}=\left(3^4\right)^{100}=81^{100}\\ 4^{300}=\left(4^3\right)^{100}=64^{100}\\ Vì:81^{100}>64^{100}\left(Do:81>64\right)\\ \Rightarrow3^{400}>4^{300}\)
\(d,10^{20}=\left(10^2\right)^{10}=100^{10}\\ Vì:100^{10}>20^{10}\left(Do:100>20\right)\\ \Rightarrow10^{20}>20^{10}\)
\(e,99^{20}=\left(99^2\right)^{10}=9801^{10}\\ Vì:9801^{10}< 9999^{10}\left(Do:9801< 9999\right)\\ \Rightarrow99^{20}< 9999^{10}\)