Find S10 for -1 + -7 + -13 + -19.  Please show your work.

1 Answer | Add Yours

durbanville's profile pic

durbanville | High School Teacher | (Level 2) Educator Emeritus

Posted on

This is an Arithmetic sequence because there is a common difference between the numbers -1: -7: -13: -19:  Therefore d= -6 

Use the formula for the sum of an arithmetic sequence:

`S 10 = n/2 ( 2a + (n - 1)d`

`S10 = 10/2(2(-1) + (10 - 1) ( -6))`

```S10 = 5 (-2 + (9) ( -6))`

```S10 = 5(-2 + (- 54)`

`` `S10 = 5 ( -56)`

``Therefore  S10 = -280    

 

We’ve answered 318,925 questions. We can answer yours, too.

Ask a question