Question

Find the sum of the first 30 terms for the given arithmetic sequence.

8, 1, -6, -13,...
-3107
-2805
-1705
-2508

Answer 1

Explanation:

Find the last term of the sequence.

a1 = 8

d = -7

n = 30

a30 = 8 + (n - 1)*(-7)

a30 = 8 + (30 - 1)*-7

a30 = 8 + 29*-7

a30 = 8 - 203

a30 = -195

Sum = (a + L)*n/2

Sum = (8 + -195) * 30/2

Sum = - 187 * 15

Sum = - 2805