There is no 5K or 3K resolution.
Only 4K, and its just a stupid name, LOL.
Anyway, yes it would be on your monitors packaging or manual and if you set your monitor to auto in display manager, it will select the correct one and tell you which one it is set to.
First number is the horizontal amount of pixels, the second is the vertical pixel count.
Gotcha. So Multi monitor setups, in other words, don't increase your resolution with each additional monitor and the highest resolution is 4k? Thank you
1920*1080 is know as HD resolution. Its the most common and probably the best choice consider higher res prices.
2650*1600 is a much higher res without a name, I think some companies call is HD+ or SuperHD.
3840 × 2160 is Ultra HD. Which is massive pixel density. You do not really get them other than in SOME TVs that are VERY Expensive.
Something to remember is that the resolution goes up exponentially every time the number increase.
For example :
1920x1080 = 2,073,600 Pixels. So just over 2 million.
2560x1600 = 4,096,000 Pixels. So that's just over 4 million.
3840x2160 = 8,294,400 Pixels. 8.2 Million.
As you can see the pixels exponentially increase even though the actual numbers do not seem to.
What this means is that the more pixels you have the harder a Graphics processor has to work to display and refresh these pixels.
Here are some sources you can read through for more info.
http://en.wikipedia.org/wiki/Display_resolution
http://en.wikipedia.org/wiki/4K_resolution
Any questions?