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NECO 2022 · Paper 1 · Q40

A sector of a circle subtends an angle of 90∘90^\circ at the centre of the circle. If the area of the sector is 11 cm211\text{ cm}^2, find its radius correct to two decimal places.

Worked solution (try it first)
  1. A 90∘90^\circ sector is a quarter of the circle: 90360×227r2=11\frac{90}{360} \times \frac{22}{7} r^2 = 11.
  2. So 2228r2=11\frac{22}{28} r^2 = 11, which gives r2=14r^2 = 14.
  3. r=14≈3.74r = \sqrt{14} \approx 3.74 cm, option B.

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