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

Answer:

Sum is 20,935.

Step-by-step explanation:

This is an arithmetic progression.

Sum:

$S = \frac{n}{2} (2a + (n - 1)d)$

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:

$S = \frac{79}{2} (2 \times - 8 + (79 - 1) \times 7)) \\ \\ S = \frac{79}{2} ( - 16 + 546) \\ \\ S = \frac{79}{2} (530) \\ S = 20935$