# How do I find the sum of an arithmetic sequence on a calculator?

##### 1 Answer

You can use the following general formula:

where the series has

(Ask a general question, get a general answer.)

#### Explanation:

Seems that it would be handy to have a closed form expression for the following:

where a and b are constants.

The commutative property of addition says

We can factor the

But we know closed form representations for both of these sums.

and

So

**EXAMPLE**

Suppose we wanted the following sum:

There are 9 terms in this series so

We want to find

which is, in fact, the sum of the numbers given.