Question 397031
You are right that PQ = {{{sqrt(80) = 4sqrt(5)}}}.  Remember that this is the LENGTH OF THE DIAMETER, and so to get the radius you only have to divide this by 2:
Radius = {{{ (4sqrt(5))/2 = 2sqrt(5)}}}
The equation of the circle is then {{{(x-3)^2 + (y + 2)^2 =  (2sqrt(5))^2 = 20}}}.