1/2+3/4+7/8+15/16+31/32+63/64=(1-1/2)+(1-1/4)+(1-1/8)+(1-1/16)+(1-1/32)+(1-1/64)=5-(1/2+1/4+1/8+1/16+1/32+1/64)=5-(32/64+16/64+8/64+4/64+2/64+1/64)=5-63/64=4又1/64
