\begin{array}{l}
 \left. 2 \right)q \ne 1 \\ 
 S_n = \sum\limits_{i = 1}^n {q^i } \Rightarrow qS_n = \sum\limits_{i = 1}^n {q^{i + 1} } \\ 
 qS_n - S_n = q^{n + 1} - q \Rightarrow S_n = q\frac{{q^n - 1}}{{q - 1}} \\ 
 \end{array}