(2)答:①E[y(t)] E Lx, coSoot-x2sinoot] -cosootElx, - tE[x2]=0 Ely2 (t)j=Ef[ x, cosoot-x2sinoot]2) E(x 2cos2oot-2xx2 coSOotsinoot+x22sin-oot) cos2OotE[x 2]-sin2ootE(x x2]+sinOotE LX2] (cos20ot)o2-sin2o tE[x,JE[x2]+(sin2oot) o2 (cosco t+sin2o t)o2=o 北京邮电大学网络学院罗老师编北京邮电大学 网络学院 罗老师编 • （2）答：①E[y（t）] =E［x1cosω0t－x2sinω0t］ =cosω0tE[x1]－sinω0tE[x2]＝0 • E{y2（t）}=E{[ x1cosω0t－x2sinω0t] 2} = E{x12cos2ω0t－2x1x2cosω0tsinω0t＋x22sin2ω0t} = cos2 ω0tE[x12]－sin2ω0tE[x1x2]＋sin2ω0tE［x22］ =（cos2ω0t）σ2－sin2ω0tE[x1]E[x2]+（sin2ω0t）σ2 =（cos2ω0t+sin2ω0t）σ2 = σ2