Question

How do you find the sum of the arithmetic sequence having the data given `a_1= 5`, `a_n = 3`, n = 20?

Answer 1

The information give gives you the first term, the last term and the number of terms. This means we can use the formula `S_n = (n/2)(a + t_n)`.

Explanation:

`S_20 = (20/2)(5 + 3)`

`S_20 = 10(8)`

`S_20 = 80`

Your sum is 80.