1.11: Crescent between an arc and a semicircle

The diagram shows an isosceles triangle $ABC$, where $AB = AC = 5\text{ cm}$. The arc $BEC$ is part of the circle centre $A$ and has length $6.2\text{ cm}$. The point $D$ is the midpoint of the line $BC$. The arc $BFC$ is a semi-circle centre $D$.