计算下面各题,找出规律：1/2+1/4+1/8= 1/2+1/4+1/8+1/16= 1/2+1/4+1/8+1/16+

1/2+1/4+1/8= 1-1/2+1/2-1/4+1/4-1/8=1-1/8=7/8
1/2+1/4+1/8+1/16= 1-1/2+1/2-1/4+1/4-1/8+1/8-1/16=1-1/16=15/16
1/2+1/4+1/8+1/16+1/32= 1-1/2+1/2-1/4+1/4-1/8+1/8-1/16+1/16-1/32=1-1/32=31/32
1/2+1/4+1/8+1/16+1/32+1/64+1/128+1/256=1-1/256=255/256