A circle has the equation \(x ^ { 2 } + y ^ { 2 } - 6 y - 7 = 0\).
- Find the coordinates of the centre of the circle.
- Find the radius of the circle.
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\caption{Figure 1}
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Figure 1 shows the sector \(O A B\) of a circle, centre \(O\), in which \(\angle A O B = 2.5\) radians.
Given that the perimeter of the sector is 36 cm ,