If `O` is the origin and `O Pa n dO Q` are the tangents from the origin to the circle `x^2+y^2-6x+4y+8-0` , then the circumcenter of triangle `O P Q` is `(3,-2)` (b) `(3/2,-1)` `(3/4,-1/2)` (d) `(-3/2,1)`