How can you tell by looking at the coordinates of the two triangles that δ a'b'c' is a 180° rotation of δ abc? a) the coordinates cannot prove a 180° rotation. b) the y-coordinates of the points on δa'b'c' have opposite signs from the corresponding points on δabc. c) the x-coordinates of the points on δa'b'c' have opposite signs from the corresponding points on δabc. d) both the x and y coordinates of the points on δa'b'c' have opposite signs from the corresponding points on δabc.