(20 14? As shown in the figure, there is a square plastic touchpad ABCD with a side length of 4, and the right vertex of a right triangle that is large enough is lost.
∵ quadrilateral ABCD is a square,
∴∠D=∠ABC=90，AD=AB，
∴∠ABE=∠D=90，
∫∠EAF = 90，
∴∠DAF+∠BAF=90，∠BAE+∠BAF=90，
∴∠DAF=∠BAE，
∴△AEB≌△AFD，
∴S△AEB=S△AFD，
∴ They all added the area of quadrilateral ABCF,
We can get the area of quadrilateral AECF = the area of square = 16.