2)∫DA = BA (square), ∠DAF=∠BAE=∠α. AF=AE (isosceles right triangle)
∴△DAF≌△BAE
∴BE=DF
3)∫DF bisects BE vertically
∴EF=FB
∫FB+AF = AB，AE=AF，AB=AD
∴AE+EF=AD
2AE again? =EF？
∴AE+ radical 2AE=AD
4)∵ The left and right sides of this quadrilateral are equal to? What are the upper and lower sides of DF? exist
A quadrilateral is a parallelogram.