$解：由秦九韶公式得：$
$ \begin{aligned} S&=\sqrt{\frac{1}{4}\left\{(\sqrt{7})^2×(2\sqrt{2})^2-[\frac {(\sqrt{7})^2+(2\sqrt{2})^2-3^3}2]^2 \right\}} \\ &=\sqrt{\frac{1}{4}[7×8-( \frac{7+8-9}{2} )^2]} \\ &= \sqrt{\frac{47}{4}} \\ &= \frac{\sqrt{47}}{2} \\ \end{aligned}$
$ $
