Given five equaldisks placed symmetrically about a given center, what is the smallest radius for which the radius
of the circular area covered by the five disks is 1? The
answer is ,
where
is the golden ratio, and the centers of the disks , ..., 5 are located at

The golden ratio enters here through its connection with the regular pentagon. If the requirement that the
disks be symmetrically placed is dropped (the general disk
covering problem), then the radius for disks can be reduced slightly to 0.609383... (Neville 1915).