简答题:已知离散型随机变量X的概率分布为
 
且E(X)=0．
(1)求a，b；
(2)求E[X(X+1)]．

A <img src="https://www.beizhujiaoyu.com/uploads/202208/162089345619991.png" width="24" height="40" /> B <img src="https://www.beizhujiaoyu.com/uploads/202208/162089346174301.png" width="24" height="40" /> C <img src="https://www.beizhujiaoyu.com/uploads/202208/162089346778191.png" width="24" height="40" /> D <img src="https://www.beizhujiaoyu.com/uploads/202208/162089347186811.png" width="22" height="27" />

A (1-2cosx)dx B (1+2cosx)dx C (1-cosx)dx D (1+cosx)dx

A <img src="https://www.beizhujiaoyu.com/uploads/202208/162089348187701.png" width="20" height="52" /> B 1 C 2 D <img src="https://www.beizhujiaoyu.com/uploads/202208/162089348651991.png" width="20" height="52" />

A x⁴ B 1+x⁴ C <img src="https://www.beizhujiaoyu.com/uploads/202208/162089350537801.png" width="19" height="52" />x⁴ D 5x⁴

A <img src="https://www.beizhujiaoyu.com/uploads/202208/162089351056341.png" width="17" height="32" />  B <img src="https://www.beizhujiaoyu.com/uploads/202208/162089351493501.png" width="36" height="32" />  C <img src="https://www.beizhujiaoyu.com/uploads/202208/162089351990151.png" width="17" height="32" />  D <img src="https://www.beizhujiaoyu.com/uploads/202208/162089352414901.png" width="35" height="32" /> 

A 4 B 0 C 2 D -4

A <img src="https://www.beizhujiaoyu.com/uploads/202208/162089353893081.png" width="60" height="32" />  B <img src="https://www.beizhujiaoyu.com/uploads/202208/162089354238161.png" width="60" height="32" />  C <img src="https://www.beizhujiaoyu.com/uploads/202208/162089354859201.png" width="79" height="32" />  D <img src="https://www.beizhujiaoyu.com/uploads/202208/162089355278041.png" width="79" height="32" /> 

A <img src="https://www.beizhujiaoyu.com/uploads/202208/162089355645231.png" width="20" height="52" /> B <img src="https://www.beizhujiaoyu.com/uploads/202208/162089356099041.png" width="20" height="52" /> C <img src="https://www.beizhujiaoyu.com/uploads/202208/162089356577071.png" width="19" height="52" /> D <img src="https://www.beizhujiaoyu.com/uploads/202208/162089358286091.png" width="20" height="52" /> <p> </p>

A xdx-4ydy B xdx-ydy C 2xdx-4ydy D 2xdx-8ydy

A 3x²+2xy B 3x²+y² C 2xy D 2y