1-1/2+1/4-1/8+1/16-1/32+1/64-1/128+1/256-1/512

1-1/2+1/4-1/8+1/16-1/32+1/64-1/128+1/256-1/512
这是首项为1,公比为-1/2的等比数列前10项和,
由公式即有：
1-1/2+1/4-1/8+1/16-1/32+1/64-1/128+1/256-1/512
=[1-(-1/2)^10]*1/(1+1/2)
=(2/3)*[1-(1/2)^10]
=(2/3)*1023/1024
=1023/1536
=341/512