Question

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

Answer 1

+6

Answer 2

1,728
1,452
2,028
2,268

Answer 3

are my options

Answer 4

1728 is the correct answer

Answer 5

thanks soo much (:

Answer 6

welcome. This is the approach I used:



The series can be written as (6j-3) where j varies from 1 through 24 ( or any n)
The summation of the series can therefore be written as ∑_(n=1)^n▒(6j-3)
= 6 (∑j) – 3n
=6*n(n+1)/2 -3n
Substitute n with any number you need
Substituting 24 for n yields the required result.