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Question
Which term of the progression 2, 8, 32, ... is 131072?
Sum
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Solution
a = 2
r = `8/2`
r = 4
`a_n = ar^(n - 1)`
131072 = `2 (4)^(n - 1)`
`(4)^(n - 1) = 131072/2`
`(4)^(n - 1) = 65536`
`(4)^(n - 1) = 4^8`
n − 1 = 8
n = 8 + 1
n = 9
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