∑ i = 0 n a i = a 0 1 − q n + 1 1 − q . {\displaystyle \sum _{i=0}^{n}a_{i}=a_{0}{\frac {1-q^{n+1}}{1-q}}.}
∑ i = 0 ∞ a i = a 0 1 − q . {\displaystyle \sum _{i=0}^{\infty }a_{i}={\frac {a_{0}}{1-q}}.}