13. Let a = (-wax ga + hwa, wa) be the twist associated with a screw having pitch h and axis 1 = {qa + Awa: A E R}, where all quantities are specified relative to a coordinate frame A. (a) Let B be a second coordinate frame with configuration gab SE(3). Show that the representation of the twist relative to B is given by b = Ada = Adga Ea. (b) Suppose instead that we move the screw via a rigid body trans- formation g SE(3). Show that the transformed screw can be represented by the twist $a = Adg Ea, still relative to the A coordinate frame.