a) \(21^{15}=21^{3.5}=\left(21^3\right)^5=9261^5\)

Vì \(9261>27\Rightarrow9261^5>27^5\Rightarrow21^{15}>27^5\)

b) \(15^{12}=\left(3.5\right)^{12}=3^{12}.5^{12}\)

\(81^3.125^5=\left(3^4\right)^3.\left(5^3\right)^5=3^{4.3}.5^{3.5}=3^{12}.5^{15}\)

Vì \(3^{12}=3^{12}\)mà \(5^{12}< 5^{15}\Rightarrow3^{12}.5^{12}< 3^{12}.5^{15}\Rightarrow15^{12}< 81^3.125^5\)

\(72^{45}-72^{44}=72^{44}\left(72-1\right)=72^{44}.71\)

\(72^{44}-72^{43}=72^{43}\left(72-1\right)=72^{43}.71\)

vì 72^44>72^43

=>72^44.71>72^43.71

  199²⁰ > 2003¹⁵

  72⁴⁵ - 72⁴⁴  < 72⁴⁴ - 72⁴³

giúp mik đi mà

giải thích cách làm của các bạn

sao lão có cách giải như thế

72⁴⁵-72⁴⁴ =72^45-44=72¹=72

72⁴⁴-72⁴³=72^44-43=72¹=72

so sánh 2 lũy thừa bằng nhau

+Ta co : 72⁴⁵-7⁴⁴=72¹=72

              72⁴⁴-72⁴³=72¹=72

Do 72=72

Vay 72⁴⁵-72⁴⁴=72⁴⁴-72⁴³

\(72^{45}-72^{44}=72^{44}\left(72-1\right)=72^{44}.71\)

\(72^{44}-72^{43}=72^{43}\left(72-1\right)=72^{43}.71\)

\(Vì\) \(72^{44}.71>72^{43}.71\)

\(\Rightarrow72^{45}-72^{44}>72^{44}-72^{43}\)

72⁴⁵ - 72⁴⁴ = 72^{45 - 44} = 72¹

72⁴⁴ - 72⁴³ = 72^{44 - 43} = 72¹

Vì 72¹ = 72¹ nên 72⁴⁵ - 72⁴⁴ = 72⁴⁴ - 72⁴³

Học tốt!!!

Ta có :

72⁴⁵ - 72⁴⁴ = 72⁴⁴.72 - 72⁴⁴ = 72⁴⁴(72 - 1) = 72⁴⁴.71

72⁴⁴ - 72⁴³ = 72⁴³.72 - 72⁴³ = 72⁴³(72 - 1) = 72⁴³.71

Vì 72⁴⁴ > 72⁴³ nên 72⁴⁴.71 > 72⁴³.71

=> 72⁴⁵ - 72⁴⁴ > 72⁴⁴ - 72⁴³ 

ghgghfjg