# 11.5.4. Arithmetic Series

If the sum of terms of an arithmetic sequence is identified by

- A
- B
- C567
- D

### Example

If the sum of terms of an arithmetic sequence is identified by

### Solution

To find the thirteenth term in the sequence, when we know a formula for the sum of the first

Alternatively, we can find the formula for the

Comparing this with the equation we have been given, we can solve for

By equating coefficients, we can see that

Using this formula, we can calculate