G3.3 In the figure, $A B C D$ is a square, $A D E$ is an equilateral triangle and $E$ is a point outside of the square $A B C D$. If $\angle A E B=\alpha^{\circ}$, determine the value of $\alpha$. (Reference: $\mathbf{1 9 9 1}$ FI1.1)
$\begin{array}{l}\alpha^{\circ}=\frac{180^{\circ}-90^{\circ}-60^{\circ}}{2}(\angle \mathrm{s} \text { sum of isos. } \Delta) \\ \alpha=15\end{array}$