方法一:用公式1/2+(1/2)^2+(1/2)^3+(1/2)^4+(1/2)^5+(1/2)^6+(1/2)^7+(1/2)^8
=1/2[1-(1/2)^8]/(1-1/2)= 1-(1/2)^8=255/256
方法二:1/2+(1/2)^2+(1/2)^3+(1/2)^4+(1/2)^5+(1/2)^6+(1/2)^7+(1/2)^8
=1/2+(1/2)^2+(1/2)^3+(1/2)^4+(1/2)^5+(1/2)^6+(1/2)^7+(1/2)^8+(1/2)^8-(1/2)^8
=1-(1/2)^8=255/256