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The diagram shows a sector \(O A B\) of a circle, centre \(O\) and radius 12 cm . The angle \(A O B\) is \(\frac { 2 } { 3 } \pi\) radians.
- Find the exact length of the \(\operatorname { arc } A B\).
- Find the exact area of the shaded segment enclosed by the arc \(A B\) and the chord \(A B\).