Check the picture below.
[tex]\textit{equation of a circle}\\\\ (x- h)^2+(y- k)^2= r^2 \qquad center~~(\stackrel{1}{ h},\stackrel{4}{ k})\qquad \qquad radius=\stackrel{2}{ r} \\\\[-0.35em] ~\dotfill\\\\ (x-1)^2~~ + ~~(y-4)^2~~ = ~~2^2\implies (x-1)^2~~ + ~~(y-4)^2~~ = ~~4[/tex]
