Formulas. In Cartesian coordinates, the open disk of center (,) and radius R is given by the formula = {(,): + <} while the closed disk of the same center and radius is given by ¯ = {(,): + ()}. The area of a closed or open disk of radius R is πR 2 (see area of a disk).. Properties. The disk has circular symmetry.. The open disk and the closed disk are not topologically equivalent (that is ...

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