2 The diagram shows a sector \(O A B\) of a circle with centre \(O\).
\includegraphics[max width=\textwidth, alt={}, center]{f4f090a1-7e36-4993-a49e-b6e7e8589057-2_341_371_968_815}
The radius of the circle is 20 cm and the angle \(A O B = 0.8\) radians.
- Find the length of the arc \(A B\).
- Find the area of the sector \(O A B\).
- A line from \(B\) meets the radius \(O A\) at the point \(D\), as shown in the diagram below.
\includegraphics[max width=\textwidth, alt={}, center]{f4f090a1-7e36-4993-a49e-b6e7e8589057-2_344_371_1747_815}
The length of \(B D\) is 15 cm . Find the size of the obtuse angle \(O D B\), in radians, giving your answer to three significant figures.