Here is a picture of a tile floor that hasn’t been finished yet. It needs some more of the gray tiles. The two lines running through the center of the floor are like mirrors. Each gray tile in the finished floor will have a mirror image across EACH of the two lines. So begin putting in gray tiles until they all have their proper reflections. Keep in mind that, as you add tiles, each new tile must also have its double reflection. You may think that the whole floor will end up gray, but it won’t. You’ll see.
In the above figure, the original gray tiles are shaded light gray and the added gray tiles are dark gray.