$9\mathrm{.}19$ Using phasors, find:$1.($a$)3$cos$(20$t$+10)5$cos$(20$t$30)2.($b$)40$sin$50$t$+30$cos$(50$t$45)3.($c$)$Answer$20416330100401$j$$j$0$j$1$j$1$j$1+$j$20$sin$4001$t$5+10$cos$(400$t$+60)5$sin$(400$t$20)$