Dell Alienware M11x R3 (Early 2011) - Manual (Page 37)

CHAPTER 2: GETTING TO KNOW YOUR LAPTOP
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F5 — Decrease Display Brightness
Press to decrease the brightness of the display.
F7 — Mute on/off
Press to mute or unmute the sound.
F8 — Decrease volume
Press to decrease the volume level.
F9 — Increase volume
Press to increase the volume level.
F10 — Rewind or Play previous track
Press to rewind or play previous track.
F11 — Play or Pause
Press to play or pause a track.
F12 — Fast Forward or Play next track
Press to fast forward or play the next track.