## College Algebra (11th Edition)

$3\sqrt{5}$ units
To find the distance between the two points, we use the distance formula: $d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}$ We plug in the points $(2,\ -3)$ and $(-1,3)$: $d=\sqrt{(-1-2)^{2}+(3--3)^{2}}$ $=\sqrt{(-3)^{2}+6^{2}}$ $=\sqrt{9+36}$ $=\sqrt{45}$ $=\sqrt{9*5}$ $=3\sqrt{5}$ Thus the distance and hence the radius is $3\sqrt{5}$.