impulse response

(a) Show that the spectrum of an AP(2) model with real poles can be obtained by the cascade connection of two AP(1) models with real coefficients.
(b) Compute and plot the impulse response, ACS, PACS, and spectrum of the AP models with p1 = 0.6, p2 = -0.9, and p1 = p2 = 0.9.