Question

. Find the sum of the first 20 terms of the
arithmetic sequence 27, 22, 17, ....

Answer 1

Explanation:

a = 27

n = 20

d = -5

L20 = 27 + (n - 1)*d

L20 = 27 + (20-1)*_5

L20 = 27 + 19*-5

L20 = -68

Sum = (a + L)*n/2

Sum = (27 - 68)*20/2

Sum = -41 * 10

Sum = - 410