First, calculate angle OAB:

\(\angle OAB = \frac{\pi}{2} - \frac{\pi}{5} = \frac{3\pi}{10}\)

Calculate the area of sector CAB:

\(\text{Area of sector } CAB = \frac{1}{2} \times \left(\frac{3\pi}{10}\right) \times 5^2 = 11.78\)

Calculate OA using the sine rule:

\(OA = \frac{5}{\sin \frac{\pi}{5}} = 8.507\)

Calculate the area of sector COD:

\(\text{Area of sector } COD = \frac{1}{2} \times (3.507)^2 \times \frac{\pi}{5} = 3.86\)

Calculate the area of triangle OAB:

\(\Delta OAB = \frac{1}{2} \times 5 \times 8.507 \times \sin \frac{3\pi}{10} = 17.20 \text{ or } 17.21\)

Calculate the shaded area:

\(\text{Shaded area} = 17.20 \text{ or } 17.21 - 11.78 - 3.86 = 1.56 \text{ or } 1.57\)