Question

How do you find the sum of the arithmetic sequence given a1=58, an=-7, n=26?

Answer 1

`S_26 = 663`

Explanation:

`S_n = (A_1 + A_n)n/2`

`=> S_26 = (58 + -7)26/2`

`=> S_26 = 51*13`

`=> S_26 = 663`