This article provides the steps for using the Display Link software solution to extend the Mac Mini to a third display. The third display generally will be a classroom TV or Projector with a dual monitor instructors station.
Login to Mac Mini
Click Spotlight Search Icon
Search DisplayLink Manager. Click to run.
This will send display to the third monitor, which is likely a TV or projector (or both).
After running, the Display Link icon will appear in the taskbar. Click the icon to set personal preferences. Select “Launch automatically after logging-in” for the software to start automatically every time you log-in.