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To connect a VGA external monitor or a projector to display a copy of the LCD screen do as root:

xrandr --output LVDS --auto --output VGA --auto --output TMDS-1 --auto

For this to work, your /etc/X11/xorg.conf file should have:

Section "Monitor"
Identifier  "TVOutput"
Option      "Ignore" "true"
EndSection

If the projector supports the LCD resolution (1600x1050), the copy will be exact. Otherwise it will display the upper left part of the LCD screen. To return back to LCD only:

xrandr --output LVDS --auto --output VGA --off --output TMDS-1 --off

Note that if you do fullscreen on acroread or ooffice, it uses the LCD native resolution. If you want to change the resolution, you do for example:

xrandr -s 1024x768

You can see the available LCD and VGA resolutions using xrandr -q.