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\pi (a + b + c)^2 <=12T

Source: Mathematics Regional Olympiad of Mexico Center Zone 2015 P6

November 12, 2021
geometryGeometric Inequalities

Problem Statement

We have 33 circles such that any 22 of them are externally tangent. Let aa be length of the outer tangent common to a pair of them. The lengths bb and cc are defined similarly. If TT is the sum of the areas of such circles, show that π(a+b+c)212T\pi (a + b + c)^2 \le 12T .
Note: In In the case of externally tangent circles, the common external tangent is the segment tangent to them that touches them at different points.