1a) Show that the circle with the equation x^2 + y^2 - 2ax - 2ay + a^2 = 0 touches both the x axis and the y axis.

b) Hence show that there are exactly two circles passing through the point (2, 4) and just touching the x axis and y axis and give their equations.

c) State the coordinates of the centres of the two circles and give the radius of each of these circles.