সমদ্বিবাহু ট্রাপেজিয়ামের প্রতিসাম্যতা

The main symmetry of an isosceles trapezoid ABCD with legs AB, CD, that is, the defining symmetry, is that given midpoints $M, N$ of $AD, BC$ respectively, the trapezoid is symmetric about $MN$.

Notice furthermore that $MN$ is perpendicular to both $AD, BC$.