G7.2 In the figure shown, $A C D E$ is a square and $A C=B C$, $\angle A C B=90^{\circ}$. Find the area of $\triangle A B C$ if the area of $A C D E$ is $10 \mathrm{~cm}^{2}$.
$$
\triangle A B C \cong \triangle C E D \cong \triangle E C A \text { (S.A.S.) }
$$

The area of $\triangle A B C=\frac{1}{2} \times$ area of $A C D E=5 \mathrm{~cm}^{2}$