bài 2
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
bài 3
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}