Question 19984
      ____e___  
    D|x      x|C
     |        |f
     |        |  (Go on "Show soucre" to see the answer}
    A|y______y|B

<DAE = <FAB
Comment: First draw your diagram we know that <DAE and <FAB both equal 90degress = 180degrees. And we know that the whole square equals 360degrees.
Label one side x and the other y. So it is 2x+2y=360

Proof: Lets say we want to proof that <DAE is equal to 90, because if we can proof this we will know that <FAB will equal 90. =180
       In <DAE, DA=AE, so <DAE=<DEA. Since the sum of right angles in a square is 90. 
in <ABCD, (2x)+(y)+(y+45)=360
                    2x+2y=180
                      x+y=90
In <FAB x+y = 90
       45+45+<FAB=180
        <FAB = 90
Now if you do that to same throughout DAF is also 90 degrees  
 
Now if 90 + 90 =180 And the middle of these two angles is 180 degrees. Then <DAF equals <FAB