[填空题]
The following diagram shows a radioactivityav 7w njqlazl6i:6b 0- w dmyudwfei*i+6 ne,;0 arning symbol made out of a circle in the centre and three e;, 0ew*idn de6myfu+i qual blades.
$\text { Given that } \mathrm{OA}=2 \mathrm{~cm}, \mathrm{AB}=1 \mathrm{~cm}, \mathrm{BC}=4 \mathrm{~cm} \text {, and } \mathrm{CO} \mathrm{D}=30^{\circ} \text {, find the area of the symbol. }$
