\(21^{15}=\)6,812231858x1019
\(27^5.49^8=\)4,768562301x1012
nen \(21^{15}< 27^5.49^8\)
ta có \(21^{15}=\left(3.7\right)^{15}=3^{15}.7^{15}\)
\(27^5.49^8=3^{15}.7^{16}\)
Mà \(7^{15}< 7^{16}\Rightarrow21^{15}< 27^5.49^8\)
2115 = ( 3 . 7 )15 = 315 . 715
275 . 498 = 915 . 716
Vì 915 > 315 ; 716 > 715
=> 2115 < 275 . 498
\(\text{Ta có : }21^{15}=\left(3\times7\right)^{15}=3^{15}\times7^{15}\)
\(27^5\times49^8=\left(3^3\right)^5\times\left(7^2\right)^8=3^{15}\times7^{16}\)
\(\text{Vì }7^{15}< 7^{16}\text{ nên }3^{15}\times7^{15}< 3^{15}\times7^{16}\)
\(\Rightarrow21^{15}< 27^5\times49^8\)