a)138 .   ( − 1 0 )     <         0

b ) 627 .   ( −  3 )     <       627

c ) ( −  72 )   .  8     <       −  72

Câu a:

3^39 và 11^21

3^39 < 3^40 = (3^4)10 = 81^10 < 121^10 = 11^20 < 11^21

Vậy 3^39 < 11^21

Câu b:

A = 72^45 - 72^44 = 72^44.(72 - 1) = 72^44.71

B = 72^44 - 72^43 = 72^43.(72 - 1) = 72^43.71

A > B

a) Ta có:

16^19=(2⁴)¹⁹=2⁷⁶                       ;             8²⁵=(2³)²⁵=2⁷⁵

Vì 76>75 nên 2⁷⁶>2⁷⁵. Vậy 16¹⁹>8²⁵

b) Ta có:

72⁴⁵-72⁴⁴=72(72⁴⁴-72⁴³)

Vậy 72⁴⁵-72⁴⁴ > 72⁴⁴-72⁴³

^{c) chịu}

a, Ta có:16^19=(2^4)^19=2^76

8^25=(2^3)^25=2^75

Vì 2^75<2^76 nên 8^75<16^19

b,Ta có:72^45-72^74=72(72^44-72^73)

=>72^45-72^44>72^44-72^43 

c,MÌNH GIẢI PHẦN NÀY SAU NHÉ!

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

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

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

72^45-72^44=72^44.7-72^44=72^44.(7-1) (1)

72^44-72^43=72^43.7-72^43=72^43.(7-1) (2)

Từ (1),(2)=>72^44.(7-1)>72^43(7-1)

=>72^45-72^44>72^44-72^43

Tick nhé

\(72^{45}-72^{44}=72^{44}\left(72-1\right)=71.72^{44}\\ 72^{44}-72^{43}=72^{43}\left(72-1\right)=71.72^{43}\\ Vì:72^{44}>72^{43}\Rightarrow72^{44}.71>72^{43}.71\\ Nên:72^{45}-72^{44}>72^{44}-72^{43}\)