If is the height of and a side of the inscribed regular hexagon and the area of the larger hexagon is , find the sum of the areas of the red triangles.
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Using the law of sines on △ A B C we obtain:
4 h ∗ = sin ( α ) a ⟹ sin ( α ) = 4 h ∗ a ⟹ h ∗ = 4 h ∗ a b ⟹ b = a 4 h ∗ 2 .
Using the law of cosines ⟹ a 2 + a b + b 2 = 1 2 h ∗ 2 ⟹ a 2 + 4 h ∗ 2 + a 2 1 6 h ∗ 4 = 1 2 h ∗ 2 ⟹ a 4 − 8 h ∗ 2 a 2 + 1 6 h ∗ 4 = 0 ⟹
( a 2 − 4 h ∗ 2 ) 2 = 0 ⟹ a = 2 h ∗ ⟹ b = 2 h ∗ ⟹ a + b = 4 h ∗ ⟹
the area of the larger hexagon A = 2 4 3 h ∗ 2 = h ∗ 4 + 4 3 2 ⟹ h ∗ 4 − 2 4 3 h ∗ 2 + ( 1 2 3 ) 2 = 0 ⟹ ( h ∗ 2 − 1 2 3 ) 2 = 0 ⟹ h ∗ 2 = 1 2 3 ⟹ h = 2 4 2 7
⟹ The sum of the areas of the red triangles ∑ j = 1 6 ( A r e d ) j = 6 ( 2 1 ) ( 2 3 h ∗ 2 ) = 6 3 h ∗ 2 = 6 3 ( 1 2 3 ) = 6 ∗ 1 2 ∗ 3 = 2 1 6 .