Question

what is the sum of the geometric sequence -3 18 -108 if there are 8 terms

Answer 1

if you can determine your common ratio, then theres a simple enough formula for it:\[S=\frac{1-r^n}{1-r}\]

Answer 2

I got 119973 is that right?

Answer 3

@amistre64

Answer 4

is that a typo @amistre64

Answer 5

he left out the first term -3

Answer 6

its -3 * (-6)^8 - 1
----------
-8 - 1

Answer 7

So did I get it wrong?

Answer 8

yes

Answer 9

Is it 719,835?

Answer 10

(-6)^8 = 1679616
1679616 -1 = 1679615
1679615 / -9 = -186623.9

Answer 11

now multiply that by -3 to get the answer

Answer 12

ah yes, first term missed it

Answer 13

That can't be right?

Answer 14

why not?

Answer 15

559,871?