Question

determine the sum of the geometric series 7+35+75+...+t₈

Answer 1

The sequence should be

7,35,175, ....... , t₈

As common ratio is 5

So S₈

That is 7+35+175+........+t₈

We have

a=7

r=5

n=8

Use $S_n=a_1.\frac{1-r^n}{1-r}=7.\frac{1-5^8}{1-5}$

$\boxed{S_n=683592}answer$