1 .AC and BD intersect at point O and G 1 point =DF, AC and BF are parallel, DG 1=G 1F, that is, point G and G1point are coincident points, and the angle GCE is 45 degrees. Triangle DBF is a right triangle, GB=GF=DG, triangle GBE is equal to triangle GEF, angle GEF=45 degrees, and triangle GEC is an isosceles right triangle. That is EG=CG, and EG is perpendicular to CG.

2. If the triangle BEF rotates around point B, it can still be proved that EG = CG and EG is perpendicular to CG. (omitted)