We are given that ∠E and ∠B are right angles and C is the midpoint of AD.
- Angle BCA is congruent to Angle DCE (Vertical Angles are Congruent) and Triangle ABC is congruent to DEC (SAS (side-angle-side)).
- Vertical angles are angles across from each other when two lines intersect. Vertical angles are always congruent. ACB and DEC are a pair of vertical angles, and BCD and ACE are a pair of vertical angles.
- Side-Angle-Side (SAS) is a congruence shortcut for triangles. When two pairs of congruent sides an one pair of congruent angles (between the sides) are in two triangles, we can assume the triangles are congruent.