Question

Given the sequence 9, 15, 21, which of the following is equivalent to \[\sum_{n=5}^{8} a_n\]

54
102
144
168

Answer 1

whats the upper limit of the summation? is it 9, 8 or g?

Answer 2

8

Answer 3

whats our 5th term? 6th term? and 7th term?

Answer 4

We know that it increases by 6 every term, and 3rd termi s 21. 4th term will then be 27, 5th term is 33.

Answer 5

What you are doing here is you get 5th, 6th, 7th, 8th term then add them all up.

Answer 6

oh.
So is that what the a_n means?
That was the part that had be confused

Answer 7

a sub n means sequence a at the nth term.