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Find the area of the shaded portion of the semicircular figure.

Mathematics
JAMB 1984

Find the area of the shaded portion of the semicircular figure.
  • A. \(\frac{r^2}{4}(4 \pi - 3 \sqrt{3})\)
  • B. \(\frac{r^2}{4}(2 \pi - 3 \sqrt{3})\)
  • C. \(\frac{1}{2}r^2 \pi\)
  • D. \(\frac{1}{8}r^2 \sqrt{3}\)
  • E. \(\frac{r^2}{4}(4 \pi - 3 \sqrt{3})\)
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Correct Answer: Option B
Explanation
Asector = \(\frac{60}{360} \times \pi r^2\)

= \(\frac{1}{6} \pi r^2\)

A\(\bigtriangleup\) = \(\frac{1}{2}r^2 \sin 60^o\)

\(\frac{1}{2} r^2 \times \frac{\sqrt{3}}{2} = \frac{r^2\sqrt{3}}{4}\)

A\(\text{shaded portion}\) = Asector -
A\(\bigtriangleup\)

= (\(\frac{1}{6} \pi r^2 - \frac{r^2\sqrt{3}}{4})^3\)

= \(\frac{\pi r^2}{2} - \frac{3r^2\sqrt{3}}{4}\)

= \(\frac{r^2}{4}(2 \pi - 3 \sqrt{3})\)

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