1+1/2+(1/2)^2+(1/2)^3+(1/2)^4+(1/2)^5+..........+(1/2)^2008=(1-(1/2)^2009)/(1-1/2)=2(1-(1/2)^2009)
发现 这个实际上是以首项为1,公比为1/2的等比数列的和Sn=a1(1-q^n)/(1-q)1+1/2+(1/2)^2+(1/2)^3+(1/2)^4+(1/2)^5+..........+(1/2)^2008=1*(1-0.5^2009)(1-0.5)=2(1-0.5^2009)