1 The diagram shows a sector \(O A B\) of a circle with centre \(O\) and radius 5 cm .
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The angle between the radii \(O A\) and \(O B\) is \(\theta\) radians.
The length of the \(\operatorname { arc } A B\) is 4 cm .
- Find the value of \(\theta\).
- Find the area of the sector \(O A B\).