Giải thích các bước giải:
$\text{Bài 10:}$
$\text{a, A= 1 + 3 +}$ $3^{2}$ $+ 3^{3}$ $+ 3^{4}$ $+ 3^{5}$ $+ 3^{6}$ $+ 3^{7}$
$\text{3A= 3 +}$ $3^{2}$ $+ 3^{3}$ $+ 3^{4}$ $+ 3^{5}$ $+ 3^{6}$ $+ 3^{7}$ $+ 3^{8}$
$\text{b, 3A - A = 3 +}$ $3^{2}$ $+ 3^{3}$ $+ 3^{4}$ $+ 3^{5}$ $+ 3^{6}$ $+ 3^{7}$ $+ 3^{8}$ $- 1 - 3 - 3^{2}$ $-3^{3}$ $-3^{4}$ $- 3^{5}$ $- 3^{6}$ $- 3^{7}$
$\text{2A = }$ $3^{8}$ $-1^{}$
$\text{A = }$ $(3^{8}$ $-1)^{}$ $: 2^{}$
$\text{Bài 11:}$
$\text{a, Q = 1 + 3 +}$ $3^{2}$ $+...+3 ^{2006}$
$\text{3Q = 3 +}$ $3^{2}$ $+ 3^{3}$ $+ ... +3^{2007}$
$\text{b, 3Q - Q = }$ $\text{3 +}$ $3^{2}$ $+ 3^{3}$ $+ ... +3^{2007}$ $\text{- 1 - 3 -}$ $3^{2}$ $-...-3 ^{2006}$
$\text{2Q =}$ $3^{2007}$ $- 1^{}$
$\text{Q =}$ $(3^{2007}$ $- 1)^{} $$: {2}$
