The Pink Area

Geometry Level 1

On the equilateral triangle, several blue unit circle sectors are constructed. What is the pink area?

3 π \sqrt{3} - \pi 3 π 2 \sqrt{3} - \frac{ \pi}{2} 3 \sqrt{3} 3 + π \sqrt{3} + \pi

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1 solution

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Eli Ross Staff
Dec 21, 2016

We can combine the 3 circular sectors to obtain a circular sector of radius 1 and central angle 6 0 + 6 0 + 6 0 = 18 0 60 ^ \circ + 60 ^\circ + 60^\circ = 180^\circ . This is a semicircle which has area 1 2 × π × 1 2 = π 2 \frac{1}{2} \times \pi \times 1^2 = \frac{ \pi}{2} .

The equilateral triangle has a base of 2, and a height of 3 \sqrt{3} , so it has an area of 1 2 × 2 × 3 = 3 \frac{1}{2} \times 2 \times \sqrt{3} = \sqrt{3} .

Since the purple area is equal to the equilateral triangle minus the circular sectors, it has an area of 3 π 2 \sqrt{3} - \frac{\pi}{2} .

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