R()=m7f()(-)d f()(-)d+x1()f(-r)t 2()(-)d+2f()(+r)d E Xf(a=Ecos(oot)u(o=f(ou(o) 则有 R([)=lim/(1)(t-r)dt =mf(0)f(+)t =lmf(0)(-)d 把(O)(+x) 1 所以R(z)=R(z) 17解题过程 A f(o 2lsin(220x1)-sin(18001 A A A 所以P 功率谱 ∞0(o\Axb(0+20m)+(-200)+6(0+180x)+(a-1800) 功率谱如图所示 200x-180( ) () ( ) () ( ) () ( ) () ( ) () ( ) 2 1 11 2 0 2 11 11 0 2 2 2 11 11 0 0 2 0 1 lim 1 lim 1 lim cos 2 τ τ τ τ τ τ ω τ →∞ − →∞ − →∞ = − ⎡ ⎤ = −+ − ⎢ ⎥ ⎣ ⎦ ⎡ ⎤ = −+ + ⎢ ⎥ ⎣ ⎦ = ∫ ∫ ∫ ∫ ∫ T T T T T T T T T R f t f t dt T f t f t dt f t f t dt T f t f t dt f t f t dt T E 又 f () ( ) () () t E tut f tut = = cos ω0 1 ( ) 则有 ( ) () ( ) () ( ) () ( ) () ( ) 2 2 2 2 2 1 1 0 2 1 1 2 1 lim 1 lim 1 lim 1 lim τ τ τ τ τ →∞ − →∞ − →∞ →∞ − = − = + = − = + ∫ ∫ ∫ ∫ T T T T T T T T T T T R f t f t dt T f t f t dt T f t f t dt T f t f t dt T 所以 ( ) ( ) 2 1 0 1 cos 2 4 τ = = τ ωτ E R R 6-17 解题过程： （4） ( ) sin 2200 sin 1800 ( )( ) 2 = − ⎡ π π ⎤ ⎣ ⎦ A f t tt 所以 22 2 884 =+= AAA P 功率谱 ( ) ( )( )( )( ) 2 2200 2200 1800 1800 8 ω = + +− ++ +− πδω π δω π δω π δω π ⎡ ⎤ ⎣ ⎦ A P 功率谱如图所示 P (ω) −2200π −1800π 1800π 2200π 2 8 A π 2 8 A π 2 8 A π 2 8 A π