[填空题]
The following diagram shg:zac:y5zj v kq ;w43rows a ons.e /eq8h2d qitk 33rxs(v)t km3 2aright-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.