1/2+1/4+1/8+1/16+1/32+1/64+1/128

1/2+1/4+1/8+1/16+1/32+1/64+1/128
1/2+1/4+1/8+1/16+1/32+1/64+1/128

1/2+1/4+1/8+1/16+1/32+1/64+1/128
等比数列求和公式：Sn=a1(1-q^n)/(1-q) =(a1-an*q)/(1-q) (q≠1)
一共7项：1/2·（1-（1/2）^7）/(1-1/2)=127/128

答：这是等比数列求和问题，首项为1/2，公比为1/2
1/2+1/4+1/8+1/16+1/32+1/64+1/128
=A1(1-q^n)/(1-q)
=(1/2)(1-1/2^n)/(1-1/2)
=1-1/2^n
=1-1/2^7
=1-1/128
=127/128

=64/128+32/128+16/128+8/128+4/128+2/128+1/128
=(64+32+16+8+4+2+1)/128
=127/128

64/128+32/128+16/128+8/128+4/128+1/128=125/128

用等比数列的求和公式就可以求出来。此题比较特殊，最后的结果等于：1-1/128=127/128，在往后加项那就等于1减去最后一项。