Dell Alienware M14x (Early 2011) - Manual (Page 39)

CHAPTER 2: GETTING TO KNOW YOUR LAPTOP
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F5 — Decrease display brightness
Press <Fn><F5> to decrease the brightness of the display.
F6 — Eject
Press <Fn><F6> to eject the disc from the optical drive.
F7 — Mute sound playback
Press <Fn><F7> to mute or unmute the sound.
F8 — Decrease volume
Press <Fn><F8> to decrease the volume level.
F9 — Increase volume
Press <Fn><F9> to increase the volume level.
F10 — Rewind or play previous track
Press <Fn><F10> to rewind or play previous track.
F11 — Play or pause
Press <Fn><F11> to play or pause a track.