1.当四边形为凸四边形时性质如图1,在四边形ABCD中,过顶点A的内角平分线分别与过顶点B、D的内角平分线交于点E、F,过顶点C的内角平分线分别与过顶点D、B的内角平分线交于点G、H;过顶点A的外角平分线分别与过顶点B、D的外角平分线交于点E′、F′,过顶点C的外角平分线分别与过顶点D、B的外角平分线交于点G′、H′,则 1. When the quadrilaterals are convex quadrilaterals, the properties are as shown in Fig.1. In the quadrilateral ABCD, the bisector of the inner angle of the vertex A is bisecting the bisector of the inner angle of the vertices B and D, respectively, at points E and F, and the bisector of the inner angle of the vertex C Respectively, with the vertex D, B bisecting the angle of the inner corner of the intersection of points G, H; over the apex of the outer bisector bisect the outer corner of the overbite points B, D intersect at points E ’, F’ The bisection lines are respectively intersected with the outer corners of the over-peak points D and B at points G ’and H’