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What is the sum of the first eight terms of the geometric series 2 + 6 + 18 + 54 + … ?

What is the sum of the first eight terms of the geometric series 2 + 6 + 18 + 54 + … ?
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What is the sum of the first eight terms of the geometric series 2 + 6 + 18 + 54 + … ?

User Bongs
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Hello,

u_(1) =2\\ u_(2) =2*3\\ u_(3) =2*3^2\\ ... u_(8) =2*3^7\\ \sum_(i=0)^7\ 2*3^i\\ =2(1+3+3^2+...+3^7)\\ =2* (3^8-1)/(3-1)\\ =2* (6560)/(2) \\ =6560
User Terrywb
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