离散型随机变量X平方的数学期望,即E[X^2]怎么求?
比如X-202
P0.40.30.3
E【X】=(-2*0.4)+(0*0.3)+(2*0.3)=-0.2
E【X^2】=?
是不是=(-2*0.4)^2+(0*0.3)^2+(2*0.3)^2