<Li> The diagonals divide each other into segments with lengths that are pairwise equal; in terms of the picture below, AE = DE, BE = CE (and AE ≠ CE if one wishes to exclude rectangles). </Li> <P> If rectangles are included in the class of trapezoids then one may concisely define an isosceles trapezoid as "a cyclic quadrilateral with equal diagonals" or as "a cyclic quadrilateral with a pair of parallel sides" or as "a convex quadrilateral with a line of symmetry through the mid-points of opposite sides". </P> <P> In an isosceles trapezoid the base angles have the same measure pairwise . In the picture below, angles ∠ ABC and ∠ DCB are obtuse angles of the same measure, while angles ∠ BAD and ∠ CDA are acute angles, also of the same measure . </P> <P> Since the lines AD and BC are parallel, angles adjacent to opposite bases are supplementary, that is, angles ∠ ABC + ∠ BAD = 180 ° . </P>

What are the properties of an isosceles trapezoid