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

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Answer 1 · 2016-03-15T03:58:49

1728

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#