## kobeni-chan one year ago Find the sum of a finite geometric sequence from n = 1 to n = 6, using the expression −2(5)^(n − 1).

1. kobeni-chan

@Nnesha

2. kobeni-chan

I know you're supposed to use Sn= a1 - an(r) / 1-r, and I had a1=-2 and an (or a6) = -6250. But when I tried to solve I didnt get any of my multiple choice answers.

3. Nnesha

formula is $\huge\rm s_n = \frac{ a_1(1-r^n )}{ 1-r }$ where r is common ratio n is number of terms

4. kobeni-chan

Oh I must've gotten the wrong formula :( So r is 5 and n is 6, right?

5. Nnesha

yep

6. kobeni-chan

Oh I got it now. Thank you! :)

7. Nnesha

np :-)