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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]

Disk with
  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 .