There is a series of circles with the same diameter in a rectangle large enough, so that the circle can cover every point in the rectangle (each point can be covered two or more times), and the number of circles is as small as possible. So is the figure formed by the line connecting the centers of the circles a regular hexagon? How to prove or simply explain it?
I know that hexagons have the highest space utilization, but don't know if it can be generalized to this conclusion.