Question

6. Find the sum of the geometric series.
a1=-9 a5=-729 r=-3

Answer 1

Sn = -9(1-(-3)^n)/4

Explanation:

Since r < 1, the sum of nth term of a geometric sequence is expressed as;

Sn = a(1-r^n)/1-r

a is the first term

n is the number f terms

r is the common ratio

An = -9(1-(-3)^n)/1-(-3)

Sn = -9(1-(-3)^n)/4

Hence the sum of the nth term of the series is Sn = -9(1-(-3)^n)/4