Given the equations of twe circles
C_1 : x^2 + y^2 −6x−4y + 9 = 0 and C_2 : x^2 + y^2 −2x−6y + 9.
(a) Find the equation of the circle C_3 which passes through the centre
of C_1 and through the point of intersection of C_1 and C_2 .
(b) The equations of two tangents from the origin to C_1 and the lenght
of each tangent.