How to mirror displays when mac connected to HDTV

When your mac is connected to HDTV, you got to drag mac application windows to right most to make them appear on the TV.  To avoid this and to mirror whatever you are viewing in your mac on your TV,  follow these instructions:

System Preferences > Displays > Arrangement > Check Mirror Displays

Make sure you have connected to your mac to HDTV, otherwise the Arrangement tab may not be visible.