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IMAS 2024/2025 Upper Primary Division - First Round Question 22

IMAS · IMAS 2024/2025 Upper Primary Division - First Round

Question 22

A fractal is a pattern that repeats forever, and every part of it, regardless of how zoomed in or zoomed out you look at the picture, will pretty much look similar to the whole image. Koch’s curve is a fractal that has infinite length but no area, generated by the following process, as shown in the diagram below:

• At iteration 0, draw a horizontal line segment that has length 1.
• At each of iterations 1, 2, …, each line segment from the previous iteration is divided into three equal segments, and the middle line segment is replaced by the two sides of an equilateral triangle of the same length as the segment being removed.

Question illustration

Let $T_n$ denote the length of the curve obtained at iteration $n$. What is the least integer $n$ such that $T_n>5$?