Wedges in a triangle 1

Geometry Level 2

Three 6 0 60^{\circ} -sectors of a unit circle pack neatly inside an equilateral triangle.

The side length of this triangle can be written as A + B C , A+\frac{B}{\sqrt{C}}, where A , B , C A, B, C are integers with C C square-free.

What is the value of A + B + C ? A+B+C?


The answer is 6.

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4 solutions

David Vreken
Sep 30, 2018

Label the points as shown below, and draw E F EF as the bisector of the sector and also draw B C BC .

Since A B C \triangle ABC is a unit equilateral triangle, B C = 1 BC = 1 , and since D E = B C DE = BC , D E = 1 DE = 1 .

As a radius of the sector, E F = 1 EF = 1 , and as a bisector of the 60 ° 60° angle, F E G = 30 ° \angle FEG = 30° , and as a tangent, E F G \angle EFG is a right angle. Therefore E G = 1 cos 30 ° = 2 3 EG = \frac{1}{\cos 30°} = \frac{2}{\sqrt{3}} .

The side length D G DG is therefore D E + E G = 1 + 2 3 DE + EG = 1 + \frac{2}{\sqrt{3}} , so A = 1 A = 1 , B = 2 B = 2 , and C = 3 C = 3 , and A + B + C = 6 A + B + C = \boxed{6} .

Can we rearrange the sectors because given its equilateral triangle and sectors also of 60° ?

Sanjay R Gayan - 2 years, 5 months ago

Why 1 + 2/√3 equals 1+2+3?🤔 Need help

Üler Angus - 2 years, 3 months ago

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The problem says the side length is in the form of A + B C A + \frac{B}{\sqrt{C}} and is asking for A + B + C A + B + C .

David Vreken - 2 years, 3 months ago
Jeremy Galvagni
Sep 29, 2018

The exact side length is 1 + 2 3 1+\frac{2}{\sqrt{3}} so the answer is 1 + 2 + 3 = 6 1+2+3=\boxed{6} .

"The area can be written as..." please change area to side length, or it is quite confusing.

X X - 2 years, 8 months ago

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Thanks. Thinking of several problems simultaneously.

Jeremy Galvagni - 2 years, 8 months ago

Which meaning of "soon" were you thinking of? >:-]

C . - 2 years, 7 months ago

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lol. Two posted solutions are better than or equivalent to mine. I have nothing to add.

Jeremy Galvagni - 2 years, 7 months ago
K T
Oct 18, 2018

The y-coordinates of the 3 apexes are 0, 1 and cos 60°. Their mean must be the center of the triangle, 1 + 1 2 3 3 \frac{1+\frac{1}{2}\sqrt{3}}{3} , so the height of the triangle is 3 times this h = 1 + 1 2 3 h=1+\frac{1}{2}\sqrt{3} , and the side s = 2 h 3 = 2 3 + 1 s=\frac{2h}{\sqrt{3}}=\frac{2}{\sqrt{3}}+1 , so the answer is 1+2+3=6

C .
Oct 19, 2018

Since i think noone has managed to over-complicate things as much as i usually do, here's how i solved this:

Since EGN is a sector of a unit circle, EK = 1, and since N E G = 6 0 \angle NEG = 60^\circ then A E K = 3 0 \angle AEK = 30^\circ , and AE = 2 * AK. Using Pythagoras, 3 × A K 2 = E K 2 = 1 3\times AK^2 = EK^2 = 1 so A K = 1 3 AK=\frac{1}{\sqrt3} . Since AE = 2 * AK, A E = 2 3 AE =\frac{2}{\sqrt3} .

Due to symmetry, B F = C D = A E = 2 3 BF = CD = AE =\frac{2}{\sqrt3} . And C J = C D D J = 2 3 1 CJ = CD - DJ = \frac{2}{\sqrt3} -1 .

Extending FL until it meets BC at P, we have L D P = M D J = 6 0 \angle LDP = \angle MDJ = 60^\circ . Since ABC is equilateral, then A B C = 6 0 \angle ABC = 60^\circ , and since B F P = H F L = 6 0 \angle BFP = \angle HFL = 60^\circ then F P B = L P D = 6 0 \angle FPB = \angle LPD = 60^\circ , therefore the LPD triangle is also equilateral.

Thus B C = B P + C D D P = B F + C D ( F P F L ) = 2 3 + 2 3 ( 2 3 1 ) = 1 + 2 3 BC = BP + CD - DP = BF + CD - (FP - FL) = \frac{2}{\sqrt3} + \frac{2}{\sqrt3} - (\frac{2}{\sqrt3} - 1) = 1 + \frac{2}{\sqrt3} . So A = 1 , B = 2 , C = 3 A=1, B=2, C=3 , and A + B + C = 6 A + B + C = \boxed{6} .

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