Write your conclusion in part D as a theorem, and prove the theorem using a two-column proof. When you write the proof, refer to the diagram you created in part A. As part of the proof, you will have to construct a line through point A parallel to BC Mark the point where the new line intersects the angle bisector, BD, and label the point E Take a screenshot of the construcion, save it and insert the image in the space below before you begin your written proof.