简便计算:1/2+3/4+7/8+15/16+31/32+63/+127/218
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1/2+3/4+7/8+15/16+31/32+63/+127/128
=1-1/2+1-1/4+1-1/8+1-1/16+1-1/32+1-1/+1-1/128
=7-(1/2+1/4+1/8+1/16+1/32+1/+1/128)
=7-1/2(1-1/2^7)/(1-1/2)
=7-127/128
=6又1/128
