Aeneas ha scritto:$S_X(f)=4,-3<=f<2 => S_X(f-5)=4,2<=f<7$
come mai questa espressione non figura nella tua?
Sto sbagliando?
$S_X(f)=4,-3<=f<-2->S_X(f-5)=4,-3<=f-5<-2<=>2<=f<3$
Poi ti rispondo pure per l'altro punto:
$Z(t)=X(t)+Y(t)=X(t)(1+cos(10pit+Phi))$
$R_Z(tau)=E{X(t)X(t+tau)(1+cos(10pit+Phi))(1+cos(10pi(t+tau)+Phi))}$=
$E{X(t)X(t+tau)[1+cos(10pit+Phi)+cos(10pi(t+tau)+Phi))+cos(10pit+Phi)cos(10pi(t+tau)+Phi))]}$=
$E{X(t)X(t+tau)[1+cos(10pit+Phi)+cos(10pi(t+tau)+Phi)+1/2cos(10pitau)+1/2cos(10pi(2t+tau)+2Phi)]}$=
$R_X(tau)[1+1/2cos(10pitau)]$ poichè $int_{0}^{2pi}cos(10pit+Phi)dPhi=int_{0}^{2pi}cos(10pi(t+tau)+Phi)dPhi=int_{0}^{2pi}cos(10pi(2t+tau)+Phi)dPhi=0$
Per cui
$S_Z(f)=S_X(f)+1/4S_X(f-5)+1/4S_X(f+5)=S_X(f)+S_Y(f)$