Explanation
3, 6, 9,..., 36.
a = 3, d = 3, i = 36, n = 18
Sn = n/2
[2a + (n - 1)d
SS18 = 18/2
[2 x 3 + (18 - 1)3]
= 9[6 + (17 x 3)]
= 9 [6 + 51] = 9(57)
= 513
3, 6, 9,..., 36.
a = 3, d = 3, i = 36, n = 18
Sn = n/2
[2a + (n - 1)d
SS18 = 18/2
[2 x 3 + (18 - 1)3]
= 9[6 + (17 x 3)]
= 9 [6 + 51] = 9(57)
= 513