Notes
trisected hexagon solution

Solution to the Trisected Hexagon Puzzle

Trisected Hexagon

This regular hexagon has been split into thirds. What’s the angle?

Solution by Trigonometry, Regions in a Regular Hexagon, and Area of a Triangle

Trisected hexagon annotated

With the points labelled as above, the regions AHGA H G and ABCA B C are each one sixth of the hexagon. Therefore, the triangle GFAG F A is one sixth of the hexagon. Triangle FEAF E A is half of the blue region so is also one sixth of the hexagon. Therefore, by the area of a triangle, triangles FEAF E A and GFAG F A must have the same “base”, so GFG F and FEF E have the same length.

Angle FA^GF \hat{A} G can then be computed using trigonometry, since GAG A has length 3\sqrt{3} times that of GEG E, so angle FA^GF \hat{A} G is given by tan 1(123)\tan^{-1}\left(\frac{1}{2\sqrt{3}}\right). Then angle CA^DC \hat{A} D is the same, and so since angle CA^G=60 C \hat{A} G = 60^\circ, we have that angle DA^FD \hat{A} F is (to 33 decimal places):

60 2tan 1(123)=27.796 60^\circ - 2 \tan^{-1}\left(\frac{1}{2\sqrt{3}}\right) = 27.796^\circ