因为随机变量X的所有概率之和为1,所以P{X=1}+P{X=2}+...+P{X=n}=1(n趋近于无穷大)。即:C(2/3)^1+C(2/3)^2+...+C(2/3)^n
=C[(2/3)^1+(2/3)^2+...+(2/3)^n]
=C2/3(1-(2/3)^n)/(1-2/3)
=2C=1,所以C=1/2。
P=P{X=1}+P{X=2}+`````=C(2/3)+C(2/3)^2+``````
=C[(2/3)-0]/[1-2/3](等比数列)=2C=1
则C=1/2