1/2 + 3/4 + 7/8 + 15/16 + 31/32 + 63/64 + 127/128=(1- 1/2)+(1-1/4)+...+(1-1/128)=7-(1/2+1/4+...+1/128)(括号内为等比数列,a1=1/2,q=1/2;s7=(1/2)(1-1/2^7)/(1-1/2)=1-1/128)=7-(1-1/128)=6又1/128