
Disk (mathematics)
Plane figure, bounded by circle / From Wikipedia, the free encyclopedia
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In geometry, a disk (also spelled disc)[1] is the region in a plane bounded by a circle. A disk is said to be closed if it contains the circle that constitutes its boundary, and open if it does not.[2]
Plane figure, bounded by circle

diameter D
radius R
center or origin O
For a radius, , an open disk is usually denoted as
and a closed disk is
. However in the field of topology the closed disk is usually denoted as
while the open disk is
.