Center (geometry)
= Center
{disambiguate=geometry}
{title2=$\mathbf c$}
= Centre
{synonym}
The center of a <circle> or <sphere> is the unique point $\mathbf c$ at the fixed positive <radius> $R$ from every point of that <circle> or <sphere>. In <Cartesian coordinates>, its equation is $|\mathbf x-\mathbf c|^2=R^2$. In the <complex plane>, a <circle> has equation $|z-c|^2=R^2$; <completing the square> identifies $c$ as its center. For example, $|z+b|^2=R^2$ has center $-b$.