Question

What is the sum of the arithmetic sequence 3, 11, 19 ..., if there are 26 terms?
A. 1,222
B. 1,261
C. 2,486
D. 2,678

Answer 1

\( \color{Black}{\Rightarrow 0.5n(a_1 + a_n) }\)

First you find \(a_{26}\)

Answer 2

what numbers do I plug in where?

Answer 3

To find a26:

\( \color{Black}{\Rightarrow a_{26} = 3 + 8(26 - 1) }\)

Then plug a26 in an

Answer 4

i don't understand..
a26=225
now what?

Answer 5

\( \color{Black}{\Rightarrow a_{26} = 3 + 200 }\)

\( \color{Black}{\Rightarrow a_{26} = 203 }\)

Back to the formula.

\( \color{Black}{\Rightarrow S = 0.5(26)(3 + 203) }\)

Answer 6

so the answer is D?

Answer 7

Yes