Question

What is the sum of the geometric sequence -4, 24, -144 .. if there are 8 items.
I know they are going up by -12.

Answer 1

no its -6.

Answer 2

common ratio = 24/-4 = -6
no. of terms = 8
first term = -4
\[Sum = \frac{a(1-r^n)}{1-r} = \frac{(-4)(1-(-6)^8)}{1-(-6)} = ...?\]