Question

What is the sum of the geometric sequence 3, 15, 75, … if there are 8 terms?

Answer 1

The sum of a geometric sequence is:
`G_s=(a_1-a_(n+1))/(1-r)`

Explanation:

First, find the 9th term where `r=5`:

`a_9=3(5)^(9-1)=1,171,875`

Now, insert the values into the formula:

`G_s=(3-1,171,875)/(1-5)=292,968`

hope that helped!