Question

What is the sum of the arithmetic sequence 3, 9, 15..., if there are 26 terms?
Someone explain what I'm doing wrong here?

Answer 1

\[S_n=\frac{ n }{ 2 }(a_1+a_n)\]

Answer 2

That's the equation, right?

Answer 3

I'm getting 377 but that's not one of the choices on the quiz I'm doing.

Answer 4

What else would it be?

Answer 5

My bad, aN should be s(26), you need to find s(26) which is

d=6

an=3+(25)6=153

now plug that back in

Answer 6

n=26

but aN=153

Answer 7

Okay so it's 2028.

Answer 8

yes

Answer 9

Alright, thanks, bud!

Answer 10

np man