1/2+1/4+1/8+1/16+.+1/2048
=1/2+(1/2-1/4)+(1/4-1/8)+(1/8-1/16)+……+(1/1024-1/2048)
=1/2+1/2-1/4+1/4-1/8+1/8-1/16+……+1/1024-1/2048
=1/2+1/2-1/2048
=1-1/2048
=2047/2048
1/2+1/4+1/8+1/16+.+1/2048
=1/2+(1/2-1/4)+(1/4-1/8)+(1/8-1/16)+……+(1/1024-1/2048)
=1/2+1/2-1/4+1/4-1/8+1/8-1/16+……+1/1024-1/2048
=1/2+1/2-1/2048
=1-1/2048
=2047/2048