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DeRet Geometri Tak Hingga

S~ = ²log x + (²log x)^3 + (²log x)^5 + ... = 2/3

a = ²log x
r = (²log x)^3 / ²log x
r = ²log² x

S~ = 2/3
a/(1 - r) = 2/3
²log x / (1 - ²log² x) = 2/3
Kali silang
3 . ²log x = 2 - 2 . ²log² x
2 . ²log² x + 3 . ²log x - 2 = 0
(2 . ²log x - 1)(²log x + 2) = 0
²log x = 1/2 ---> x = 2^1/2 = √2
²log x = -2 ---> x = 2^-2 = 1/2² = 1/4

Nilai x yg memenuhi :
√2 dan 1/4