Question

what is the sum of the geometric sequence -3 , 18, -108 if there are 7 terms?

Answer 1

The answer choices are:
-719,835
-119,973
119,973
719,835

Answer 2

Yes

Answer 3

Noo

Answer 4

There are four answer choices

Answer 5

Sum of n terms = a1 r^n - 1
-------
r - 1

whre a1 = first term and r = common ratio

Answer 6

so plug in a1 = 8 , r = -6 and n = 7

Answer 7

sorry a1 = -3

Answer 8

So it's -3(-6)^7-1 over -6-1?

Answer 9

not exactly - work out the (-6)^7 first then subtract 1
then divide by -7
finally multiply by -3

Answer 10

I got -119,973 is that right?

Answer 11

I should have written the (r^n - 1) like that - in parentheses

Answer 12

yes

Answer 13

Okay thank you very much

Answer 14

yw

Answer 15

oh = press best response

Answer 16

I did