$\;x^2\,+\,y^2\,-\,12x\,+\,16y\,-\,1\,=\,0\,$
A equação geral da circunferência de centro (a,b) e raio R:
$x^2\,+\,y^2\,+\,mx\,+\,ny\,+\,p\,=\,0\,$. Então
$\left.\begin{array}{rcr}\,a\,=\,-{\large \frac{m}{2}}\;\Rightarrow\;a\,=\,-{\large \frac{(-12)}{2}}\;\Rightarrow\;a\,=\,6 \;& \\ \,b\,=\,-{\large \frac{n}{2}}\;\Rightarrow\;b\,=\,-{\large \frac{(+16)}{2}}\;\Rightarrow\;b\,=\,-8 & \\ \end{array} \right\}$ $\;\Rightarrow \; \boxed{\;C\,(6\,,\,-8) \;}$
$p\,=\,a^2\,+\,b^2\,-\,R^2\;\Rightarrow $ $\;-1\,=\,6^2\,+\,(-8)^2\,-\,R^2\;\Rightarrow$ $\;R^2\,=\,101\;\Rightarrow\;\boxed{\;R\,=\,\sqrt{101}\;}$