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CC & ET Expanded (Posted on 2018-12-29) Difficulty: 3 of 5

See the problem as posed originally here.

Triangle T has area A and sides of length a,b, and c.

Given 3 concentric circles of radius a,b,c, respectively, find the areas of the largest and smallest equilateral triangles with a vertex on each circle in terms of the given variables.

No Solution Yet Submitted by broll    
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Smallest one Comment 2 of 2 |
A,B,C are vertex and O is center of the circles, with a rotation of 60° degrees of the segment OA about C you get a bigger equilateral triangle OO'C where O'B is equal to OA. 
Then also OBO' is an abc triangle.

From there using two times theorem of cosine I got a formula for the asked Area 

A=(1/4)*[a^2+b^2+c^2]-sqr3*AreaT(abc)

Edited on January 13, 2019, 8:35 am
  Posted by armando on 2019-01-13 06:35:15

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