设离散随机变量X的分布列为:
X-202
P0.40.30.3
求:(1)E(X);
(2)E(X2);
(1)E(X)=∑3i=1xipi=(-2)×0.4+0×0.3+2×0.3 =-0.2 (2)E(X2)=3i=1xi2pi=(-2)2×0.4+02×0.3+22×0.3=2·8. (3)E(3X3+5)=3E(X3)+5=33i=1xi3pi+5=3[(-2)3× 0.4+03×0.3+23×0.3]+5=2·6.
设离散随机变量X的分布列为:
X-202
P0.40.30.3
求:(1)E(X);
(2)E(X2);
(1)E(X)=∑3i=1xipi=(-2)×0.4+0×0.3+2×0.3 =-0.2 (2)E(X2)=3i=1xi2pi=(-2)2×0.4+02×0.3+22×0.3=2·8. (3)E(3X3+5)=3E(X3)+5=33i=1xi3pi+5=3[(-2)3× 0.4+03×0.3+23×0.3]+5=2·6.