UV=acXY+adX+bcY+bdE(UV)=acE(XY)+adEX+bcEY+bdEU=aEX+bEV=cEY+dEU*EV=acEXEY+adEX+bcEY+bd因此两式相减得E(UV)=EU*EV=ac[E(XY)-EXEY]=acCov(XY)不明白可以追问,如果有帮助,请选为满意回答!