Triangle CDA is the image of triangle ABC after a 1800 rotation around the midpoint of segment AC. Triangle ECB is the image of triangle ABC after a 1800 rotation around the midpoint of segment BC. Explain why ABCD and ABEC are parallelograms.
Identify at least two pairs of congruent angles in the figure and explain how you know they are congruent.
Explain how to use what you know about the sum of the angles in a triangle to figure out the sum of the angles of quadrilateral ABED.