=(1-1/2-1/4-1/8-1/16-1/32-1/64-1/128-1/256 -1/256)+1/256
=(1-1/2-1/4-1/8-1/16-1/32-1/64-1/128-1/128)+1/256
=...
=0+1/256
=1/256(3/4+1/5)+(4/5+1/6)+(5/6+1/7)+(6/7+1/8)+(7/8+1/9)+(8/9+1/10)+(9/10+1/11)+(10/11+1/12)=(1-1/4+1/5)+(1-1/5+1/6)+......+(1-1/11+1/12)=8-1/4+1/12)=7又5/6