B2
a, Ta có : 5^23 = 6 . 5^22 > 5.5^22 = 5^23
Vậy 6.5^22 > 5^23
b,Ta có : 7.2^13 < 8,2^13 = 2^3 . 2^13 = 2^16
Vậy 7.2^13 < 2^16
c, Ta có : 21^15 = (3.7)^15 = 3^15 . 7^15
27^5 = (3^3)^5 = 3^15
49^8 = (7^2)^8 = 7^16
Vì 3^15 . 7^15 < 3^15 . 7^16
Nên 21^15 < 27^5 . 49^8
Vậy 21^15 < 27^5 . 49^8
B4
72^45-72^44 và 72^44-72^43
72^45-72^44= 72^45.(72-1)=72^45.71
72^44-72^43=72^43.(72-1)= 72^43.71
=>72^45-72^44> 72^44-72^43
B5
16^x < 128 ^ 4
24x<228
4x<28
=> x<7=>x ∈{0,1,2,3,4,5,6}
5^x+1 . 5^x+2<10^18:2^18
=>5x+3<5^18
3x + 3 ≤ 18
=> 3(x + 1)≤ 18
=> x + 1 ≤ 6
=> x ≤ 5 => x ∈ {0;1;2;3;4;5}
cho mình 5 sao nhé :))))
