Its possible that the low beam filimant is burnt out or if you have separate lamps for high and low, that could be it too. You can lookup your vehicle below to see if you have separate high and low beam lamps - this may help - see sources and related links.
High beam light is out!
Check the bulb Check to see if you are getting power to the socket
Usually it will be either the dimmer switch or a connecter if the low beam works and highs don't.
Low beam bulb is burnt out. Replace it.
Yes
there are two diff types of bulbs. High beam and low beam bulbs. If your low beam doesn't work then you need to replace those lights because they are probably blown.
Bulbs blew
Possibly the high beam element for the passenger side is broken. There are two elements inside those lightbulbs, one for low beam, the other for high beam.
No the high beam filament is independent from the low beam filament You can run them seperately or together . it depends on how the lights are set up. For instance if you have your high beam on you may have your lows running at the same time, however if your low beam is on low beam setting, your highs are always turned of It sounds like you may need to look at your fuses or your switch.
It's a Cadillac, what do you expect?
Usually yes.