由题意令:S=1/3+1/3^2+1/3^3+1/3^4+1/3^5+1/3^6+1/3^7+1/3^8那么:3S=1+ 1/3+1/3^2+1/3^3+1/3^4+1/3^5+1/3^6+1/3^7所以:2S=3S-S=1 - (1/3)^8解得:S=[1 - (1/3)^8]/2=3280/6561