A circle has equation x2+y2=10y−6x−9x^2 + y^2 = 10y - 6x - 9x2+y2=10y−6x−9
By completing the square in x x\,x and in yyy, express the equation of the circle in the form (x−a)2+(y−b)2=k(x - a)^2 + (y - b)^2 = k(x−a)2+(y−b)2=k where aaa, b b\,b and k k\,k are constants to be found.
Write down the coordinates of the centre of the circle and its radius.