I just bought a new 29 inch wide LG monitor (29UM58). It wants a resolution not available on my Mac Mini running El Capitan. What? 2560 x 1080 (whatever!) and as a result I get a 4 inch black area on each side of the screen. It would be great to use the whole screen but LG tech support is no help. They tell me to hook it up via HTM cable. I did dat! I do know where to select resolutions in Preferences but the needed resolution is not there to select. Questions are: where do these choices come from? Can I glom the right resolution from another computer? Anyone help me out here?