31. In the following figure, $A D=A B, \angle D A B=\angle D C B=\angle A E C=90^{\circ}$ and $A E=5$. Find the area of the quadrangle $A B C D$.
31 Ans: 25.
Upon rotating $A E D$ anticlock wise $90^{\circ}$ through $A$, we get a square. Thus the area is $5^{2}=25$.