MathDB
max of distances, sequences of figures by pyramids , triangles of midpoints

Source: Puerto Rico TST 2019.6

September 16, 2021
geometry3D geometrypyramidinequalities

Problem Statement

Starting from a pyramid T0T_0 whose edges are all of length 20192019, we construct the Figure T1T_1 when considering the triangles formed by the midpoints of the edges of each face of T0T_0, building in each of these new pyramid triangles with faces identical to base. Then the bases of these new pyramids are removed. Figure T2T_2 is constructed by applying the same process from T1T_1 on each triangular face resulting from T1T_1, and so on for T3,T4,...T_3, T_4, ...
Let D0=max{d(x,y)}D_0= \max \{d(x,y)\}, where xx and yy are vertices of T0T_0 and d(x,y)d(x,y) is the distance between xx and yy. Then we define Dn+1=max{d(x,y)d(x,y){D0,D1,...,Dn}D_{n + 1} = \max \{d (x, y) |d (x, y) \notin \{D_0, D_1,...,D_n\}, where x,yx, y are vertices of Tn+1T_{n+1}.
Find the value of DnD_n for all nn.