a) Ta có : 1255 = ( 53 )5 = 515 > 514 = ( 52 )7 = 257
b) Ta có : 920 = ( 32 )20 = 340 > 339 = ( 33 )13 = 2713
c) Ta có : 354 = ( 32 )27 = 927 > 827 = ( 23 )27 = 281
\(a)\)\(125^5\)và \(25^7\)
\(125^5=\left(5^3\right)^5=5^{15}\)
\(25^7=\left(5^2\right)^7=5^{14}\)
Vì: \(15>14\)
Nên: \(125^5>25^7\)
\(b)\)\(9^{20}\)và \(27^{13}\)
\(9^{20}=\left(3^2\right)^{20}=3^{40}\)
\(27^{13}=\left(3^3\right)^{13}=3^{39}\)
Vì: \(40>39\)
\(\Rightarrow\)\(9^{20}>27^{13}\)
\(c)\)\(3^{54}\)và \(2^{81}\)
\(3^{54}=3^{2.27}=\left(3^2\right)^{27}=9^{27}\)
\(2^{81}=2^{3.27}=\left(2^3\right)^{27}=8^{27}\)
Vì: \(9>8\)
\(\Rightarrow\)\(3^{54}>2^{81}\)
