Find the sum of the first 18 terms of the series 3, 6, 9,..., 36.

Find the sum of the first 18 terms of the series 3, 6, 9,..., 36.

Answer Details

3, 6, 9,..., 36.
a = 3, d = 3, i = 36, n = 18
Sn = $\frac{n}{2}$ [2a + (n - 1)d
S18 = $\frac{18}{2}$ [2 x 3 + (18 - 1)3]
= 9[6 + (17 x 3)]
= 9 [6 + 51] = 9(57)
= 513