连结CO ,DO .
∠OAB=∠OBA=1/2 (180°−∠AOB)=30°
∠OAD=∠ODA=52.5°−30°=22.5° .
∠OBC=∠OCB=97.5°−30°=67.5° .
∠COD=60°.
S=1/2[sin120°+sin135°+sin60°+sin45° ]c² =（√2+√3）c²/2
图我帮你补上了
连结CO ,DO .
∠OAB=∠OBA=1/2 (180°−∠AOB)=30°
∠OAD=∠ODA=52.5°−30°=22.5° .
∠OBC=∠OCB=97.5°−30°=67.5° .
∠COD=60°.
S=1/2[sin120°+sin135°+sin60°+sin45° ]c² =（√2+√3）c²/2
图我帮你补上了