Find the sum of a finite geometric sequence from n = 1 to n = 7, using the expression −4(6)^n − 1.

111,325
526
782
-223,948

Question

Find the sum of a finite geometric sequence from n = 1 to n = 7, using the expression −4(6)^n − 1.

111,325
 526
 782
 -223,948

hartnn · Answer

$\large a_n = -4 (6)^{n-1}$

The sum of 'n' terms of an Geometric series is given by:
$\Large S_n = a_1 \dfrac{r^n-1}{r-1}$

where a1 is the first term = ..?
r = common ratio = ...?

hartnn · Answer

n = number of terms = 1 to 7 = 7

hartnn · Answer

if you can find a1 and r from $a_n$
then you just plug those in the formula and you'll get the sum

kidthatbro8 · Answer

i'm not very good at this... can you help me?

hartnn · Answer

i'll try :)

In,
$\Large a_n = a_1 r^{n-1}$
the 1st term is a_1 and the common ratio is 'r'

hartnn · Answer

you can also check this tutorial out: http://openstudy.com/study#/updates/503bb2a0e4b007f9003103b0

kidthatbro8 · Answer

thank you!

hartnn · Answer

did you get the answer to this problem?