Horrible Hexagons 2

Geometry Level 3

The diagram above shows a regular hexagon with side length 2 2 and two equilateral triangles inscribed in it.

The area of the shaded region can be written as a 3 b \large \frac { a\sqrt { 3 } }{ b } , where a a and b b are coprime integers. Find a b ab .


The answer is 24.

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3 solutions

The shaded region is composed of two congruent non-overlapping equilateral triangles of side length 2 sec ( 3 0 ) = 4 3 . 2\sec(30^{\circ}) = \dfrac{4}{\sqrt{3}}.

Their combined areas, and hence the area of the shaded region, is then

2 × 1 2 × ( 4 3 ) 2 × sin ( 6 0 ) = 16 3 × 3 2 = 8 3 3 . 2 \times \dfrac{1}{2} \times \left( \dfrac{4}{\sqrt{3}} \right)^{2} \times \sin(60^{\circ}) = \dfrac{16}{3} \times \dfrac{\sqrt{3}}{2} = \dfrac{8\sqrt{3}}{3}.

Thus a b = 8 × 3 = 24 . ab = 8 \times 3 = \boxed{24}.

Samuel Li
Apr 5, 2015

The area is a parallelogram with height 2 2 and base 2 × 2 3 = 4 3 3 2 \times \frac{2}{\sqrt{3}} = \frac{4\sqrt{3}}{3} . Therefore, the area is 8 3 3 \boxed{\frac{8\sqrt{3}}{3}} .

All small triangles have an area of 3 3 each of the two shaded big triangles have four such triangles. s h a d e d a r e a s = 8 3 3 . a b = . 24 \text{All small triangles have an area of}~\dfrac{\sqrt3}{3}\\\text{each of the two shaded big triangles have four such triangles. }\\\therefore~ shaded ~~areas \\= 8*\dfrac{\sqrt3}{3}.~~~~~~~~~~ab=\large. 24

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