Question

Can someone show me how to do this?
Find the sum of the given arithmetic series.

25 + 18 + 11 + 4 + ... + (–38)

Answer 1

\[S _{n} =\frac{ n }{ 2 }(a _{1} + a _{n})\] is your formula.

n is the number of terms
a1 is the first term
an is the last term

Can you get started now? I am still here.

Answer 2

Well I got stuck because im not sure how to find the number of terms

Answer 3

any help? @mrbarry

Answer 4

\[a _{n} = a _{1} + (n-1)d\] is what we need now.

Everything has the same meaning. d is the difference between consecutive terms.
Can you roll now?

Answer 5

Oh okay I understand what I need to do