# Find the centre and radius of the circle $x^2+y^2-4x-9y-45=0$
$\begin{array}{1 1}centre = (2,4)\; and radius = \sqrt {65} \\ centre = (2,-4)\;and \;radius = \sqrt {65} \\ centre = (-2,4) \;and \;radius = \sqrt {65} \\ centre = (-2,-4)\; and radius = \sqrt {65} \end{array}$