The input to a certain amplifier is

vin$($t$)=0\mathrm{.}1$cos$(2000$t$)+0\mathrm{.}2$cos$(4000$t$+30)$vin$($t$)=0\mathrm{.}1$cos$(2000$t$)+0\mathrm{.}2$cos$(4000$t$+30),$

and the corresponding output voltage is

vo$($t$)=10$cos$(2000$t$20)+15$cos$(4000$t$+20)$vo$($t$)=10$cos$(2000$t$20)+15$cos$(4000$t$+20).$