根据分布律的性质c/3^0+c/3^1+c/3^2+……=1∴c(1+1/3+1/3^2+……)=11+1/3+1/3^2+……是等比级数其和为1+1/3+1/3^2+……=1/(1-1/3)=3/2∴c·3/2=1∴c=2/3
