Question 259845
The rule given below has to be applied for proving.
SAS (Side-Angle-Side): If two pairs of sides of two triangles are equal in length, and the included angles are equal in measurement, then the triangles are congruent. 
In rect ABCD the diagonals of the rectangles are congruent and bisect each other.
AE and EC are congruent
BE and ED are congruent
The angle containing this sides are congruent. because they are vertically opposite angles.
Hence traingle AED is congr to trangle CED