1 The diagram shows a sector \(O A B\) of a circle with centre \(O\) and radius \(r \mathrm {~cm}\).
\includegraphics[max width=\textwidth, alt={}, center]{bfe96138-9587-4efb-95c5-84c4d5eadfbe-2_382_351_379_826}
The angle \(A O B\) is 1.25 radians. The perimeter of the sector is 39 cm .
- Show that \(r = 12\).
- Calculate the area of the sector \(O A B\).