Question 470206
Let T be the point of tangency given in the problem.  Then radius PT is perpendicular to the tangent as given.  Since chord AB is parallel to the tangent line, it is also perpendicular to radius PT. Let point C be the intersection of AB and PT.  Then Triangle PCB is a right triangle, with PC = 3 (as given), and CB = 6 (half of chord AB, since PT also bisects AB).  Hence radius {{{r = sqrt(3^2 + 6^2) = 3sqrt(5)}}}, by direct use of the Pythagorean theorem.