What is the sum of the arithmetic sequence 3, 9, 15…, if there are 24 terms?

1 Answer
Mar 15, 2016

1728

Explanation:

We must first find the common difference, r.

r = t_2 - t_1

r = 9 - 3

r = 6

Now, we can use the formula s_n = n/2(2a + (n - 1)d)

n = 24

a = 3

r = 6

s_24 = 24/2(2(3) + (24 - 1)6)

s_24 = 12(6 + 138)

s_24 = 12(144)

s_24 = 1728