Question

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

you know a = 10, n = 8 and term 8

so use the formula below

\[T _{n} = ar^{n -1}\]

\[781250 = 10 \times r^7\]

solve for r

when you have found r the sum of the x terms is

\[S _{n} = \frac{a( r^n -1)}{r -1}\]

Answer 2

Thank you :)