3.4: Logo of three sectors with variable radii

In this question all lengths are in centimetres and all angles are in radians.
The diagram shows a company logo. Each part of the logo is a sector of a circle with centre .
Sector has radius .
Sector has radius .
Sector has radius .
The shaded region has area and perimeter .
It is given that and can vary.
(a)[4]
Show that .
(b)[5]
Use differentiation to find the minimum possible area of the logo.
