r = 1/2 + 1/4 + 1/8 = 1/16 + 1/32 + 1/64
2 X R = 1 + 1/2 + 1/4 +............. + 1/64
2 x r - r = 1 - 1/64
r = 63/64
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r= \(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}\)
=> 2r = \(1+\frac{1}{2}+\frac{1}{4}+...+\frac{1}{32}\)
=> 2r - r = \(1-\frac{1}{64}\)
Vậy r =\(\frac{63}{64}\)
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