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?

Answer 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)

Answer 2

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

Answer 3

If it is not in your text, burn your text.
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