Triangle ABC is a right triangle. Point D is the midpoint of side AB, and p A D E C B The proof, with a missing reason, proves that the measure of ECB is Statement Reason mZADE = 68 Given m2DAE = 90 Definition of a right angle mZAED = 22 Triangle Sum Theorem DE joins the midpoints of AB and AC Given DE is parallel to BC ? ZECB ZAED Corresponding angles are m2ECB 22 Substitution property