Question

What is the sum of a 7 term geometric series if the first term is -11 and the last term is -45,056 and common ratio -4

Answer 1

well if you know the 1st term and common ratio you can use the formula

\[a_{n} = a_{1} \times r^{n - 1}\]

you know a1 = -11 and r = -4 and n = 7

so substitute and calculate away

Answer 2

To get the sum of the first \(n\) terms,

\[S_n =a_1\frac{(1-r^n)}{(1-r)}\]