Find the sum of the first 18 terms of the arithmetic sequence whose nth term is an = 3n - 1.

495

Step-by-step explanation:

In order to find the sum of the first 18 terms you have to find the 18th term and the first term using the equation given.

a1=3 (1) - 1 a1=2

a18=3 (18) - 1 a18 = 53

Then plug in 53 for an, 18 for n, and 2 in for a1 in the sum equation: Sn=n/2 (a1+an)

Sn=18/2 (2+53) Solve for sn = 495