Let $Z_t$ denote white noise with standard deviation . In each of the following cases, derive the spectral density function for the process $X_t,$ and evaluate it for the given frequency $\omega$, giving your answer to three decimal places.

Part (a) $X_t = Z_t + Z_{t-1},$ at $\omega =$


Part (b) $X_t = Z_t + Z_{t-1} + Z_{t-2} ,$ at $\omega =$


Part (c) $X_t = Z_t + Z_{t-1} - Z_{t-2},$ at $\omega =$