WAEC - Mathematics (1998 - No. 24)
In the diagram above, O is the center if the two concentric circle of radii 13cm and 10cm respectively. Find the area of the shaded portion in the sector with angle 120° at the center
\(\frac{1}{3}\pi cm^2\)
\(\pi cm^2\)
\(3\pi cm^2\)
\(23\pi cm^2\)
\(46\pi cm^2\)
Explanation
\(\frac{120\pi}{360}(R^2 - r^2)\)
= \(\frac{1}{3}\times \pi (13^2 - 10^2)\)
= \(\frac{1}{3}\times \pi \times 69\) = 23\(\pi cm^2\)
= \(\frac{1}{3}\times \pi (13^2 - 10^2)\)
= \(\frac{1}{3}\times \pi \times 69\) = 23\(\pi cm^2\)
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