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The area of a sector of a circle of radius 5 cm formed by an arc of length 3.5 cm is?

  • A.0.35 cm²
  • B.17.5 cm²
  • C.8.75 cm²
  • D.55 cm²

Answer: C

A sector is a triangle-like wedge whose "base" is its arc and whose "height" is the radius:

\[ A = \frac{1}{2} \times r \times \text{arc length} \]

\[ = \frac{1}{2} \times 5 \times 3.5 = 8.75 \text{ cm}^{2} \]

This form needs no angle at all. It follows from \( A = \tfrac{\theta}{2\pi}\pi r^{2} \) and \( \text{arc} = r\theta \), which combine to give exactly \( \tfrac{1}{2}r \times \text{arc} \).

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