Question

What is the sum of the first six terms of the geometric series 4 − 12 36 − . . . ?

Answer 1

The formula to use for the sum of n terms is as follows:
$S_{n}=\frac{a(1-r^{n})}{1-r}$
r = -3, n = 6.
$S_{6}=\frac{4(1-(-3)^{6})}{1-(-3)}=-728$