a,Ta có : 339 < 340 = 920 < 1120 <1121
Vậy 339 < 1121
b,
ta có2225 = (23)75 = 875
3151 > 3150 = (32)75 = 975
=> 3151 > 975 > 875
=> 3151 > 2225
c,ta có
5566 = (556)11 = 2768064062511
6655 = (665)11 = 125233227611
Vì 27680640625 > 1252332276 nên 2768064062511 > 125233227611
=> 5566 > 6655
*) \(3^{39}=\left(3^{13}\right)^3=1594323^3\)
\(11^{21}=\left(11^7\right)^3=19487171^3\)
Mà \(1594323< 19487171\)
\(\Rightarrow1594323^3< 19487171^3\)
Vậy \(3^{39}< 11^{21}\)
*) \(55^{66}=\left(55^6\right)^{11}=17680640625^{11}\)
\(66^{55}==\left(66^5\right)^{11}=1252332576^{11}\)
Mà \(17680640625>1252332576\)
\(\Rightarrow17680640625^{11}>1252332576^{11}\)
Vậy \(55^{66}>66^{55}\)