17.7, Exercises 435 Exercise 17.18 Determirte the auto-correlation secpxmcc y z [ K ; ] , the auto-rovariance sequence [ K ] asld the power cicnsity spectriirn aTS (&) of t ~ i crandom process fiom Exexcise ?.C;a) 4, ~ x 17.19 e ~ ~ ~ ~ ~ Consider the ergotlic discrete random proress 'throwing a tetrahedral die', which has marked on one side and I iiiarked 011 the other three: x[k] is the iximihr lying undcincath Delermine u , ~ q , , [ ~dzZ[&l ], and (v'")