Definition:Complex Disk

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Definition

Let $a \in \C$ be a complex number.

Let $R>0$ be a real number.


Open disk

The open (complex) disk of center $a$ and radius $R$ is the set:

$B(a, R) = \{z\in \C : |z-a| < R\}$

where $|\cdot|$ denotes complex modulus.


Closed disk

The closed (complex) disk of center $a$ and radius $R$ is the set:

$B(a, R) = \{z\in \C : |z-a| \leq R\}$

where $|\cdot|$ denotes complex modulus.


Also see