Question

Use the summation formula to find a partial sum of a series with the following properties

Geometric
a1= -11
a7= -45,056
n= 7
r= -4

Answer 1

-36,047.

Explanation:

Sum of n terms = a1 .( r^n - 1) / (r - 1)

So Sum of 7 terms = -11 . ((-4)^7 - 1 / (-4-1)

= -11 * -16,385 / -5

= -36,047.