如图．在$\text{Rt}\Delta \text{ABC}$中，$\mathit{AC}=3$，$\angle \mathit{ABC}=90°$，$\mathit{BD}$是$\mathit{\Delta ABC}$的角平分线，过点$D$作$\mathit{DE}\perp \mathit{BD}$交$\mathit{BC}$边于点$E$．若$\mathit{AD}=1$，则图中阴影部分的面积为