7/2+7/4+7/8+7/16+7/32+7/64/7/128+7/256+7/512
=7(1/2+1/4+1/8+1/16+1/32+1/64+1/128+1/256+1/512)
=7(1/2+1/4+1/8+1/16+1/32+1/64+1/128+1/256+1/512+1/512)-7/512
=7(1/2+1/4+1/8+1/16+1/32+1/64+1/128+1/256+1/256)-7/512
=7(1/2+1/4+1/8+1/16+1/32+1/64+1/128+1/128)-7/512
=7(1/2+1/4+1/8+1/16+1/32+1/64+1/64)-7/512
=7(1/2+1/4+1/8+1/16+1/32+1/32)-7/512
=7(1/2+1/4+1/8+1/16+1/16)-7/512
=7(1/2+1/4+1/8+1/8)-7/512
=7(1/2+1/4+1/4)-7/512
=7(1/2+1/2)-7/512
=7-7/512
=6+505/512
=6又505/512