upgrade screen to 1680 * 1050

No - Apple reports that this system also supports "1280 by 800, 1152 by 720, 1024 by 640, and 800 by 500 pixels at 16:10 aspect ratio; 1024 by 768, 800 by 600, and 640 by 480 pixels at 4:3 aspect ratio; 1024 by 768, 800 by 600, and 640 by 480 pixels at 4:3 aspect ratio stretched; 720 by 480 pixels at 3:2 aspect ratio; 720 by 480 pixels at 3:2 aspect ratio stretched."

If you found such a display the OS/video card or drivers would not likely support it.

As a work around you might be able to use a resolution app to achieve that scale... but it might be illegible on a laptop.

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