1 The diagram shows a sector \(O A B\) of a circle with centre \(O\) and radius 6 cm .
\includegraphics[max width=\textwidth, alt={}, center]{02e5dfac-18d7-480d-ac23-dfd2ca348cba-2_358_332_358_829} The angle between the radii \(O A\) and \(O B\) is \(\theta\) radians.
The area of the sector \(O A B\) is \(21.6 \mathrm {~cm} ^ { 2 }\).

1. Find the value of \(\theta\).
2. Find the length of the \(\operatorname { arc } A B\).