Đáp án:
$\begin{array}{l}
S = \frac{{{u_1}}}{{1 - q}}\\
1)\\
{u_1} = \frac{1}{{100}};q = \frac{1}{{100}}\\
S = 1 + 2\left( {\frac{1}{{100}} + \frac{1}{{{{100}^2}}} + ...} \right)\\
\Rightarrow S = 1 + 2.\frac{{\frac{1}{{100}}}}{{1 - \frac{1}{{100}}}} = \frac{{101}}{{99}}\\
2){u_1} = \frac{1}{2};q = \frac{1}{2}\\
\Rightarrow S = \frac{{\frac{1}{2}}}{{1 - \frac{1}{2}}} = 1\\
3)\\
S = 1 - \frac{1}{3} + \frac{1}{9} - \frac{1}{{27}} + ...\\
{u_1} = 1;q = - \frac{1}{3}\\
\Rightarrow S = \frac{1}{{1 + \frac{1}{3}}} = \frac{3}{4}
\end{array}$
