Cutting A Hexagon

Geometry Level 3

The figure above shows a regular hexagon inscribed inside a circle with center O O such that O A = 1 OA = 1 . Find the area of the shaded region.

If the area can be written as a π b c \dfrac{a\pi-\sqrt{b}}{c} , where a , b a,b and c c are integers with both a , b a,b primes , submit your answer as a + b + c a+b+c .


The answer is 13.

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1 solution

Paola Ramírez
May 4, 2016

A C AC and F B FB are perpendicular bisectors of A B O \triangle ABO \Rightarrow the areas b b and e e are equals. Then b + c + d b+c+d is equal to 1 2 \frac{1}{2} of A B O \triangle ABO area. Also b + c + d = a b+c+d=a because O A OA is perpendicular bisector of O A OA \therefore a + b + c + d a+b+c+d is equal to A B O \triangle ABO area.

A B O \triangle ABO area is equal to 3 4 \boxed{\frac{\sqrt{3}}{4}}

Area g g is two times area f f . Area g g is equal to a sixth part of the circle's area minus A B O \triangle ABO area. This is π 6 3 4 = 2 π 3 3 12 g + f = 1.5 ( 2 π 3 3 12 ) = 2 π 3 3 8 \frac{\pi}{6}-\frac{\sqrt{3}}{4}=\frac{2\pi-3\sqrt{3}}{12}\Rightarrow g+f=1.5 \left(\frac{2\pi-3\sqrt{3}}{12}\right) =\boxed{\frac{2\pi-3\sqrt{3}}{8}}

a + b + c + d + e + f + g = 2 π 3 3 8 + 3 4 = 2 π 3 8 a+b+c+d+e+f+g=\frac{2\pi-3\sqrt{3}}{8}+\frac{\sqrt{3}}{4}=\boxed{\frac{2\pi-\sqrt{3}}{8}}

Be free of asking any question in comments

Well I think there is some mistake in stating the question

You have written that 'c' is a prime no. But '8' is not a prime no.

Nice solution though...

Archiet Dev - 5 years, 1 month ago

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It's has been edited. Thank you

Paola Ramírez - 5 years, 1 month ago

@Jason Chrysoprase here is the solution

Paola Ramírez - 5 years, 1 month ago

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Thanks Paola

Jason Chrysoprase - 5 years, 1 month ago

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