Ta có : \(A=4+2^3+2^4+2^5+...+2^{2003}+2^{2004}\)
=> \(A=2^2+2^3+2^4+...+2^{2003}+2^{2004}\)
=> \(2A=2^3+2^4+2^5+...+2^{2004}+2^{2005}\)
=> \(2A-A=\left(2^3+2^4+...+2^{2005}\right)-\left(2^2+2^3+...+2^{2004}\right)\)
=> \(A=2^{2005}-2^2\)
(làm đc từng này thôi ^^)
A = 4 + 23 + 24 + 25 + ...+ 22003 + 22004
đặt B = 23 + 24 + 25 + ...+ 22003 + 22004
2B= 24 + 25 + 26 + ....+ 22004 + 22005
2B-B= ( 24 + 25 + 26 + ....+ 22004 + 22005 ) - ( 23 + 24 + 25 + ...+ 22003 + 22004 )
B = 24 + 25 + 26 + ....+ 22004 + 22005 - 23 - 24 - 25 - ...- 22003 - 22004
B = 22005 - 23
B = 22005 - 8
=> A = 4 + B = 4 + 22005 - 8 = 22005 - 4 = .....
Đề thiếu thì phải :V