1/2+1/4+1/8+1/16+1/32+1/64+1/128+1/256=1/2+1/4+1/8+1/16+1/32+1/64+1/128+(1/128-1/256)=1/2+1/4+1/8+1/16+1/32+1/64+(1/128+1/128)-1/256=1/2+1/4+1/8+1/16+1/32+1/64+1/64-1/256=1/2+1/4+1/8+1/16+1/32+1/32-1/256=……=1-1/256=255/256