Đáp án:
$\text{ $\dfrac{1093}{729}$}$
Giải thích các bước giải:
$\text{1 + $\dfrac{1}{3}$ + $\dfrac{1}{9}$ + $\dfrac{1}{27}$ + $\dfrac{1}{81}$ + $\dfrac{1}{243}$ + $\dfrac{1}{729}$ }$
$\text{= 1 + $\dfrac{1}{2}$(1 - $\dfrac{1}{3}$ + $\dfrac{1}{3}$ - $\dfrac{1}{9}$ + $\dfrac{1}{9}$ - $\dfrac{1}{27}$ + $\dfrac{1}{27}$ - $\dfrac{1}{81}$ + $\dfrac{1}{81}$ - $\dfrac{1}{243}$ + $\dfrac{1}{243}$ - $\dfrac{1}{729}$)}$
$\text{= 1 + $\dfrac{1}{2}$(1 - $\dfrac{1}{729}$)}$
$\text{= 1 + $\dfrac{1}{2}$ . $\dfrac{728}{729}$}$
$\text{= 1 + $\dfrac{364}{729}$ }$
$\text{= $\dfrac{1093}{729}$}$
