设随机变量X的概率密度f(x)=
{1+x，-1≤x≤0；
{1-x，0
求E(X)．
E(X)=∫+∞-∞xf(x)dx =∫0-1dx+∫10x(1-x)xd =[(1/2)x2+(1/3)x3]0-1+[(1/2)x2-(1/3)x3]10=0．
设随机变量X的概率密度f(x)=
{1+x，-1≤x≤0；
{1-x，0
求E(X)．
E(X)=∫+∞-∞xf(x)dx =∫0-1dx+∫10x(1-x)xd =[(1/2)x2+(1/3)x3]0-1+[(1/2)x2-(1/3)x3]10=0．
