设随机变量X~B(6,0.4) 则E(X2)

E(x)=2.4
D(x)=np(1-p)
=6x0.4x0.6
=6x0.24
=14.4
D(x)=E(x²)-[E(x)]²
E(x²)=14,4+5.76
=20.16