Algebra (Final)

I know my answer, but I stumbled on it accidentally. I want to know exactly HOW to get my answer. The question states: In a geometric sequence, a1=12 and r=(sqrt)2. What is the approximate sum of the first 20 terms of the sequence?

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1. why worry about the approximate sum? Use your formula to get

S20 = 12((√2)^20-1)/(√2-1) = 12(1024-1)/(√2-1) = 12276/(√2-1)

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2. What's my formula? I don't know it.

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https://www.varsitytutors.com/hotmath/hotmath_help/topics/sum-of-the-first-n-terms-of-a-geometric-sequence

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bobpursley

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