[填空题]
The following diagra6gc v*j etnf /k .s+fi(heeg-a i7)qm:m shows a r2ybat . :qnl*qight-angled triangle $\mathrm{ABC}$ 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.