Question

Add the first 79 terms of this sequence:
-8,-1, 6, 13, 20, ...

Answer 1

The answer for this equation is: 7

Answer 2

Sum is 20,935.

Explanation:

This is an arithmetic progression.

Sum:

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

n is the number of terms, n = 79

S is the sum

a is the first term, a = -8

d is common difference, d = -1-(-8) = 7

substitute:

`S = (79)/(2) (2 * - 8 + (79 - 1) * 7)) \\ \\ S = (79)/(2) ( - 16 + 546) \\ \\ S = (79)/(2) (530) \\ S = 20935`