What is the sum of the geometric series 2+6+18+...+486?

asked Aug 25, 2021 180k views

4 votes

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3 votes

Answer:

728

Explanation:

2+6+18+...+486

a=2

r=6/2=3

$a_(n)=ar^(n-1)\\486=2(3)^(n-1)\\3^(n-1)=486/2=243=3^5\\n-1=5\\n=5+1=6\\S_(6)=2(3^6-1)/(3-1) \\=2(729-1)/(2)\\=728$

John Bowen answered Aug 29, 2021

5.7k points

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