The first three terms of a geometric series are 5,15,45. Find the sum of the first n terms if the nth term of this series is 10935

Trace Glass

Trace Glass

Answered question

2022-10-30

The first three terms of a geometric series are 5,15,45. Find the sum of the first n terms if the nth term of this series is 10935

Answer & Explanation

Rylan White

Rylan White

Beginner2022-10-31Added 10 answers

This is a geometric series with r = 3. First, find what term 10935 is.
5 ( 3 n - 1 ) = 10935
( 3 n - 1 ) = 2187
3 n - 1 = 3 7
n - 1 = 7
n = 8
Now use the formula for the sum of the first n terms of a geometric series:
S n = a 1 ( 1 - r n ) 1 - r
S 8 = 5 ( 1 - 3 8 ) 1 - 3 = 16400

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