Which symbol is missing? Explain your reasoning.

• tbqry'f vapbzcyrgrarff gurberz? but there are so many different encodings for it
– Sny
Commented Jan 20 at 10:43
• @SnySmartie No, not relevant to this puzzle Commented Jan 20 at 10:46
• havpbqr is my best bet now, the is element is really confusing
– Sny
Commented Jan 20 at 10:49
• @SnySmartie No sry, not relevant to that either. Commented Jan 20 at 10:53

The missing symbol is:

the number 1.

If we look at the letters in the corners of the squares...

...these form an anagram of GEOMETRIC. If we order the squares so as to spell this out (disambiguating the two Es by judging what makes the most sense), we see the following:

In other words:

$$(\frac{1}{2})^n, n ∈ N$$

This is the summand of a famous geometric series related to Zeno's paradoxes.

The terms of this series are $$\frac{1}{2}$$, $$\frac{1}{4}$$, $$\frac{1}{8}$$, $$\frac{1}{16}$$, and so on, with the more terms you add taking the total sum a little bit closer towards 1, so that over time we would say that this infinite series 'converges towards 1'. Convergence is represented by an arrow in mathematics, so in the diagram here we are being asked what this infinite geometric series will converge to - and that answer is our missing symbol: 1.

This can be seen and understood a little more clearly through the use of a diagram. Here, adding rectangles with areas equivalent to the terms in this series means that the more terms in the sequence, and the more rectangles you add, the closer you get to a complete unit square of area 1: