1/2+1/4+1/8+1/16+1/32+.+1/128=

1/2+1/4+1/8+1/16+1/32+.+1/128=
1/2+1/4+1/8+1/16+1/32+.+1/128=

1/2+1/4+1/8+1/16+1/32+.+1/128=
1/2+1/4+1/8+1/16+1/32+.+1/128= 1-1/128=127/128

用等比数列求和、x=<1/2(1-(1/2)^7)>/(1-1/2)=1-(1/2)^7即一减去二分之一的七次方