This is only an estimation of the location. It should be close, but you will likely still need to look around a bit to find it. Read the backdrop for basic instructions. Basically, I'll emphasize some important stuff here. DO NOT MOVE from where you threw your ender eye when writing down coordinates. Also, DO NOT LOOK AROUND after you have centered your crosshair on the ender eye. It is very important to accurately record where you were when you threw it and what direction it traveled. The coordinates look like XYZ: 435.5 / 64 / -163.3 The 1st number is the X coordinate, and the 3rd is Z. The part that says your direction looks like Facing: east (Towards positive X) (-100/10) The 1st number there is the direction that is important. Make sure that you move in a DIFFERENT direction than the ender eye when going to throw it a second time. Don't move in the opposite direction either, though.
This is some really basic trig type of stuff I think. Basically, take the x and y (Minecraft is weird and calls what should be y, z) and direction, and figure out the corresponding equation for a line. Do that for two different throws, and then find the intersection of the two lines. This will estimate where the stronghold is.
