In this paper,some fixed value theorems for directed areas in circular c ircumscribed pentagons are obstain ed,thus some concurrent results,including the famous Brianchon theo rem for circular circumscribed pent agons,can be deduced easily.

• 本文给出圆外切五边形中有向面积的几个定值定理,并据此推出圆外切五边形中的一些共点性结论,其中包括射影几何中著名的Brianchon定理在圆外切五边形中的情形。