1/2+1/4+1/8+1/16+1/32+1/64+1/128
=1/1-1/2+1/2-1/4+1/4-1/8+1/8-1/16+1/16-1/32+1/32-1/64+1/64-1/128
=1/1-1/128
=127/128
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\(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}+\frac{1}{128}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{8}+\frac{1}{8}-\frac{1}{16} +\frac{1}{16}-\frac{1}{32} +\frac{1}{32}-\frac{1}{64}+\frac{1}{63}-\frac{1}{128}\)
\(=1-\frac{1}{128}\)
\(=\frac{127}{128}\)
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tính nhanh p/s 1+ 5/4 + 5/8 + 5/16 + 5/32 + 5/64
