Question

What is the sum of an 8-term geometric series if the first term is −11, the last term is 859,375, and the common ratio is −5? −143,231 −36,047 144,177 716,144

Answer 1

The sum of geometric series is 716144

Explanation:

Given

First term=a_1= -11

Last term=a_8=859375

Common ration of geometric series=r= -5

And

Total terms in geometric sequence=n=8

We know that the formula for sum of geometric series is:

S_n= (a_1 (1-r^n))/(1-r)

= (-11(1-(-5)^8)/(1-(-5))

= (-11(1-5^8))/(1+5)

= (-11(1-390625))/6

=(-11(-390624)))/6

=4296864/6

=716144

So the sum of geometric series is: 716144 ..