maths----geometry

Since center of circle must lie on the perpendicular bisector of any 2 points, from point C and D, we know that center must lie on the x -axis, that is the y - coordinate of center is 0. Similarly, from point A and B, center must lie on the line x = (- 5 + 1)/2 = - 2, that is the x - coordinate of center is - 2. So center is (-2, 0).
Radius of circle = distance between center and any of the 4 points, take point C
= sqrt [(- 2 - 3)^2 + (0 - 3)^2] = sqrt (25 + 9) = sqrt 34
so equation of circle is
(x + 2)^2 + y^2 = 34
x^2 + y^2 + 4x - 30 = 0.