Question

In order to sum a geometric sequence with seven terms, how would the equation be set up?

Answer 1

do you have the equation to sum up X amount of terms in a geometric series?

Answer 2

No I do not, that is what I was inquiring about.

Answer 3

\[\huge S_n=a_1(\frac{{1-(r}^n)}{1-r})\]

Answer 4

Thank you bibby!

Answer 5

so n is the amount of terms, can you take it from here?

Answer 6

Correct. My series is -4, 24, -144 I know the common ratio is -6. So i am plugging in the values now.

Answer 7

It is a 7 term series

Answer 8

Actually, isnt the equation set up like this?

Answer 9

I don't think so

Answer 10

If you factor out the \(a_1\) from the numerator, it's the same thing

Answer 11

Interesting because when I set up the equation I get a decimal. And not a whole number.

Answer 12

I'll step through it then

Answer 13

\[\huge S_n=a_1(\frac{{1-(r}^n)}{1-r})\]
\(\huge S_n=-4(\frac{{1-(-6}^7)}{1-(-6)})=-4(\frac{{1--279936})}{1+6})\)

Answer 14

Oh wow. Nevermind. I messed up. I left out the "r" on the bottom so i was ending up with -1119748. Instead of -159964. Thank you very much! And sorry to take up lots of your time :/

Answer 15

lol, I have a bazillion sites I would have been visiting anyways, I was tabbed out, you were doing most of the work

Answer 16

Still, Thank you!

Answer 17

np np :)