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sum of the areas of the removed squares from 9 squares of unit square

Source: Eotvos 1905 p2

September 6, 2024
geometryareas

Problem Statement

Divide the unit square into 99 equal squares by means of two pairs of lines parallel to the sides (see figure). Now remove the central square. Treat the remaining 88 squares the same way, and repeat the process nn times.
(a) How many squares of side length 1/3n1/3^n remain? (b) What is the sum of the areas of the removed squares as nn becomes infinite? https://cdn.artofproblemsolving.com/attachments/7/d/3e6e68559919583c24d4457f946bc4cef3922f.png