Question

[Trần Đức]

give isosceles trapezoid abcd ( ab // cd,ab<cd) from a draw ah perpendicular ab , ah intersects bd at h . from b draw bk perpendicular ab , bk intersects ac at k a) what figure is quadrilateral ahkb?why? b) Given that E,F are the midpoints of AB, DC; I and G are respectively the intersection points of AC with BD , CH with DK . Prove that four points E,I,G,F are collincar