How can I test a display resolution that's not listed? I'm planning to give a talk at a conference, and I've been told that slides will be displayed on a screen with a resolution of "2048 x 1080 (16:9 aspect ratio)".

I want to see how my slides look at that resolution. I have a Macbook Pro (non-retina screen) running OSX Mavericks and no external display.

In System Preferences, I can choose between only two "scaled" resolutions: 1280 x 800 and 1024 x 640.

Is there a way that I can use an unlisted resolution?
To see all graphics supported modes use the alt key before clicking on Scaled in display preferences.

To see it in 19:9 use a Thunderbolt cable to a TV. (assuming you have those)

If you have a Mac like I do (MBA 2012) then using the Thunderbolt you can get up to 2560 by 1600 pixels on your HDTV.

Intel HD Graphics 4000
Dual display and video mirroring:
Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on an external display, both at millions of colors