Sum of a GP Starting from the $$m$$th Term

Sum of a GP Starting from the $$m$$th Term

## Formula

If the $$m$$th term is:

$$a_m=ar^{m-1}$$

then the sum of the next $$n$$ terms starting from the $$m$$th term is:

$$S=ar^{m-1}\frac{1-r^n}{1-r}$$

for:

$$r\ne1$$

## Usage

- Used when a GP sum starts from a term other than the first term.