1. Draw a sketch.

2. You'll get 2 sektors whose central angles are 2u and 2w respectively. You know that

The area of a segment is calculated by: Area of sector - area of right triangle.

The common side of the two triangles is calculated by:

Unfortunately LaTeX doesn't work anymore. Therefore you wasn't able to see this line:

\tan(w)=\dfrac{a \cdot \sin(x)}{b+a\cdot \cos(x)}

Re-written into the simple syntax it means:

tan(w)=(a * sin(x))/(b+a*cos(x))

3. Calculating the orange area :

4. Calculating the green area :

5. Add both areas and try to simplify this term a little bit.

Maybe you can use the property: