V(t)=5 cos wt + 2 ? Is this ac or dc ? And why ?

this is AC b/c cos is a periodic function.. think waves... the voltage is going to vary between positive 5 and negative 5 volts... so it's a low voltage signal, but still AC,   the W is for how fast it's varying and the  +2 is the off set of the wave.  

Explanation:

answer; (wage) income

answer; wireshark;