Answer:
AA similarity theorem
Step-by-step explanation:
we know that
AA (Angle-Angle) Similarity states that In two triangles, if two pairs of corresponding angles are congruent, then the triangles are similar
In this problem we have that
∠BCA=∠ECD ----> by vertical angles
∠BAC=∠DEC ---> because AB is parallel to ED (alternate interior angles)
therefore
Triangles ABC and EDC are similar by AA similarity theorem
