∠AED is a straight angle. Prove: m∠AEB = 45° A horizontal line has points A, E, D. 2 lines extend from point E. One line extends to point B and another extends to point C. Angle C E D is a right angle. Complete the paragraph proof. We are given that Ray E B bisects ∠AEC. From the diagram, ∠CED is a right angle, which measures degrees. Since the measure of a straight angle is 180°, the measure of angle must also be 90° by the . A bisector cuts the angle measure in half. m∠AEB is 45°.