[填空题]
The following diagram shows a right-angled tria3do 1-ito soc rlk pcj9j )*n944wkbk.ng ryn b6ezlx0+*le $\mathrm{ABC}$ and a sector ABD of a circle with centre $\mathrm{A}$ . The point $\mathrm{E}$ lies on [AC] such that [BE] is perpendicular to [AC]. The region R is bounded by [DE], [BE] and arc BFD.