3.17: Segment with given area and sine of the angle

In this question, all lengths are in centimetres and all angles are in radians.
The diagram shows a sector of a circle with centre and radius .
(a)[2]
It is given that the area of triangle is .
Find the value of .
(b)[4]
It is also given that the exact area of the shaded segment is .
Find the exact length of the arc .
