Question

4. What is the sum of an 8-term geometric sequence if the first term is 10 and the last term is
781,250

Answer 1

1-r^n
----- but that would imply we knew r, or at least would have to find r
1- r

Answer 2

should we divide out the 10 first?

Answer 3

78125 is left and that might indicate a base 5?

Answer 4

divide 8th term by first gives r^7
so can find r this way

Answer 5

5^7 = 78125 :)

Answer 6

I'm working on the problem now. It might take me a minute or two.

Answer 7

r = 5

Answer 8

\[A = a +ar^2+ar^3+...+ar^7\]
\[a*[A=1+r+r^2+r^3+...+r^7]\]

Answer 9

Yes, I also got r = 5.

Answer 10

i make it 976560

Answer 11

\[10*\frac{1-5^8}{1-5}=sum\]
perhaps?

Answer 12

r=5
s=10(1-5to 8)/4=976560

Answer 13

Yes, sorry I'm so slow. This is the same answer I got :)