
By solving x=y with circle We get $\begin{aligned}
& \mathrm{C}(\sqrt{2}, \sqrt{2}) \
& \mathrm{D}(-\sqrt{2},-\sqrt{2})
\end{aligned}Bysolving\mathrm{x}+\mathrm{y}=1withcirclex^2+y^2=4weset\begin{aligned}
& \mathrm{A}\left(\frac{1+\sqrt{7}}{2}, \frac{1-\sqrt{7}}{2}\right) \
& & \mathrm{~B}\left(\frac{1-\sqrt{7}}{2}, \frac{1+\sqrt{7}}{2}\right)
\end{aligned}\thereforeAreaofQuadrilateralACBD=2 \times \text { Area of } \triangle \mathrm{BCD}\begin{aligned} & =2 \times \frac{1}{2}\left|\begin{array}{ccc}\sqrt{2} & \sqrt{2} & 1 \ \frac{1-\sqrt{7}}{2} & \frac{1+\sqrt{7}}{2} & 1 \ -\sqrt{2} & -\sqrt{2} & 1\end{array}\right| \ & =2 \sqrt{14}\end{aligned}$