A Triangle on Three Incircles of a Cube

Problem

figure

As shown in the figure, the cube ABCD-EFGHABCD\text{-}EFGH has edge length 22, where EE, FF, GG, HH lie directly above AA, BB, CC, DD respectively. A point P1P_1 is chosen arbitrarily on the incircle of the square face ABFEABFE, a point P2P_2 on the incircle of the square face BCGFBCGF, and a point P3P_3 on the incircle of the square face EFGHEFGH.

Find the minimum and maximum values of

P1P2+P2P3+P3P1.|P_1P_2|+|P_2P_3|+|P_3P_1|.

Answer

Solution

Difficulty7/10
TopicsParametrization, solid geometry, Cauchy-Schwarz, AM-GM, inequality

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