How do you find the sum of a geometric sequence? (-3,18,-108... if there are 8 terms)

Question

anonymous · Answer

First find the common ratio

anonymous · Answer

thats when you deivide the second term by the first, right? so it would be -6?

anonymous · Answer

divide the second term by the first term to find the common ratio

anonymous · Answer

Yes,-6 is correct

anonymous · Answer

okay, then what?

anonymous · Answer

Now, use this

`last term = a (common ratio ^ (number of terms - 1))`

anonymous · Answer

okay, i got 839808 but thats not an answer i have to choose from.

anonymous · Answer

wait

anonymous · Answer

(-3,18,-108... if there are 8 terms)
i think now you should do this
-108 x -6 = 648
648 x -6 = -3888
-3888 x -6 = 23328
23328 x -6 = -139968

anonymous · Answer

so now
-139968 = -3 times - 6 ^n-1

anonymous · Answer

what are your options?

anonymous · Answer

my options are -719835, 719835, 119973, and -119973

anonymous · Answer

I think its 719835

anonymous · Answer

Certainly

anonymous · Answer

Great, thank you

anonymous · Answer