Given: ab//dc

prove: triangle abe similar to triangle dce

Draw the two triangles so the two triangles share point C.  It should look like a bowtie. (1) AB is parallel to DE                   Given (2) Angle A = Angle D                    If two parallel lines are cut by a transversal, alternate interior angles are equal.     Angle B = Angle E   (3) Angle BCA = Angle DCE            Vertical angles are equal. (4) Triangle BAC is similar to Triangle DEC      If 3 angles in one triangle are equal to three angles in another triangle,                                                                     the triangles are similar. (5) AB/DE = AC/EC                        If two triangles are similar, corresponding sides are proportional. Hope this helps.