DX=EX²-(EX)² 于是 EX²=1/2+1=3/2
E[X(X–Y+3)]=E(X²-XY+3X)=E(X²)-E(XY)+3EX=E(X²)-EX*EY+3EX (随机变量XY相互独立)
于是 E[X(X–Y+3)]=3/2-1*1+3=7/2
DX=EX²-(EX)² 于是 EX²=1/2+1=3/2
E[X(X–Y+3)]=E(X²-XY+3X)=E(X²)-E(XY)+3EX=E(X²)-EX*EY+3EX (随机变量XY相互独立)
于是 E[X(X–Y+3)]=3/2-1*1+3=7/2
