Regular Partitioning

Geometry Level 3

In a regular hexagon A B C D E F ABCDEF , points W W , X X , Y Y , and Z Z are on sides C D CD , B C BC , A F AF , and E F EF , respectively, in a way such that A B AB , W Z WZ , X Y XY , and E D ED are parallel and equidistant. If the side length of A B C D E F ABCDEF is 1, what is the area of hexagon W C X Y F Z WCXYFZ ?

4 3 \dfrac{4}{3} 3 2 \dfrac{\sqrt{3}}{2} 5 3 9 \dfrac{5\sqrt{3}}{9} 11 3 18 \dfrac{11\sqrt{3}}{18}

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2 solutions

Aaron Tsai
Jul 21, 2016

We draw equilateral triangles as shown above. We can split up W C X Y F Z WCXYFZ into two trapezoids. B D = 3 BD=\sqrt{3} (since it is twice the altitude of an equilateral triangle with side length 1 1 ).

Zoom into the top half of A B C D E F ABCDEF :

The smaller equilateral triangle is similar to the larger ones. We are given that A B AB , W Z WZ , X Y XY , and E D ED are parallel and equidistant, so they divide A B C D E F ABCDEF (and therefore B D BD ) into thirds. So, the altitude of the larger equilateral triangles is 3 3 \dfrac{\sqrt{3}}{3} , and the altitude of the smaller equilateral triangle is 3 6 \dfrac{\sqrt{3}}{6} . From that, we know that the smaller equilateral triangle is similar to the larger ones with a similarity ratio of 1 : 2 1:2 .

The base of the smaller equilateral triangle is 1 3 \dfrac{1}{3} (because of 30-60-90 triangle ratios). Since the similarity ratio between the smaller and larger equilateral triangles is 1 : 2 1:2 , the larger ones each have bases of 2 3 \dfrac{2}{3} . Therefore, Z W = 5 3 ZW=\dfrac{5}{3} . Since we know the height ( 3 6 \dfrac{\sqrt{3}}{6} ) and two bases of trapezoid Z W C F ZWCF (since F C = 2 FC=2 ) we can compute its area to be 11 3 36 \dfrac{11\sqrt{3}}{36} .

Since W C X Y F Z WCXYFZ is made up of two of these trapezoids, its area is 2 11 3 36 = 11 3 18 2\cdot\dfrac{11\sqrt{3}}{36}=\boxed{\dfrac{11\sqrt{3}}{18}} .

Ahmad Saad
Jul 21, 2016

Niranjan Khanderia - 4 years, 10 months ago

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