A = 1 + 2 + 22 + ...... + 29
2A = 2(1 + 2 + 22 + ...... + 29)
= 2 + 22 + 23 + ....... + 210
2A - A = (2 + 22 + 23 + ....... + 210) - (1 + 2 + 22 + ...... + 29)
A = 210 - 1
B = 5.28 = (22 + 1).28 = 22.28 + 1.28 = 210 + 28 > 210 - 1
Do đó B > A
A = 1 + 2 + 22 + 23 + ... + 29
\(\Rightarrow\)2A = 2 + 22 + 23 + ... + 210
\(\Rightarrow\)2A - A = ( 2 + 22 + 23 + ... + 210 ) - ( 1 + 2 + 22 + 23 + ... + 29 )
\(\Rightarrow\)A = 2 + 22 + 23 + ... + 210 - 1 - 2 - 22 - 23 - ... - 29
A = 210 - 1
Ta có : ( 4 + 1 ).28 = 4.28 + 28 = 28.28 + 28 = 210 + 28
\(\Rightarrow\)210 - 1 < 210 + 28 hay
A > B .
Ta có : A = 1 + 2 + 22 + 23 + ....... + 29
=> 2A = 2 + 22 + 23 + ....... + 210
=> 2A - A = 210 - 1
Mà B = 5.28 = (22 + 1) .28 = 210 + 28
Nên B > A
