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/...