Show that the equation x² + y² - 3x + 3y + 10 = 0 does not represent a circle.

Show that the equation 3x² + 3y² + 6x - 4y – 1 = 0 represents a circle. Find its centre and radius.

Show that the equation x² + y² + 2x + 10y + 26 = 0 represents a point circle. Also, find its centre.

Find the equation of the circle passing through the points

(i) (0, 0), (5, 0) and (3, 3)

(ii) (1, 2), (3, - 4) and (5, - 6)

(iii) (20, 3), (19, 8) and (2, - 9)

Also, find the centre and radius in each case.

Find the equation of the circle which is circumscribed about the triangle whose vertices are A( - 2, 3), b(5, 2) and C(6, - 1). Find the centre and radius of this circle.