Disk (mathematics)
= Disk
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{title2=$D_R$}
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= Disk
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= Euclidean disk
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A planar <Euclidean disk> consists of the points within a fixed radius of a centre, with either the open or closed boundary convention. The closed disk centered at the origin is $D_R=\{x\in\mathbb R^2:|x|\leq R\}$ and has <area> $\pi R^2$. It is the two-dimensional closed Euclidean ball; the general <closed disc> may have any dimension.