Arithmetic Series

The sum of an arithmetic series is found with the formula:

$$ S_n = \frac{n}{2}(a_1 + a_n) $$

Where $n = \lfloor \frac{a_{n, \text{end}} - a_1}{d} \rfloor + 1$. The calculator finds the last term ($a_n$) that is less than or equal to the end number you provide.

Geometric Series

The sum of a finite geometric series is found with the formula:

$$ S_n = a_1 \frac{1 - r^n}{1 - r} \quad (for, r \neq 1) $$