Cho

- Hướng dẫn giải

$A=1+2+2^2+...+2^{2007}$

$2A=2+2^2+...+2^{2007}+2^{2008}$

A = 2A$-$A = $(2+2^2+...+2^{2007}+2^{2008})$$-$$(1+2+2^2+...+2^{2007})$ = $2^{2008}-1$

Vậy $A=2^{2008}-1$