Proving 4θ = π+4sinθ: Circular Measure

[look416]

Homework Statement

A chord of a circle subtends an angle of θ radians at the centre of the circle. The area of the minor segment cut off by the chord is one eighth of the area of the circle. Prove that 4θ = π + 4 sin θ

Homework Equations

s = rθ
area of sector = 1/2 r²θ
area of minor segment = area of sector - area of triangle
= 1/2 r²θ - 1/2 ab sin θ

The Attempt at a Solution

1/2r²2π x 1/8 = area of minor segment
area of minor segment = 1/2r²θ - 1/2 ab sin θ
1/2r²2π x 1/8 = 1/2r²θ - 1/2 ab sin θ
well the problem is i don't know what is the value of ab

 

[Mentallic]

the area of the triangle is \frac{1}{2}absinC right?
The a and b are the sides of the triangle adjacent to the angle. They're the radii of the circle.