Notes, Thoughts & Puzzles

Welcome to my digital garden. Here I share informal mathematical notes, historical curiosities, solutions to interesting problems, and personal reflections on academic life.

Analysis Golden Ratio

When the Derivative Equals the Inverse: A Golden Connection

Dec 27, 2025 8 min read

We usually think of differentiation and inversion as completely different operations. But what happens if we force them to be the same? The solution to $f'(x) = f^{-1}(x)$ leads us unexpectedly to the Golden Ratio and generalized "Metallic Means".

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Calculus Geometry Challenge

Maximum Area of an Ellipse Inscribed in a Circle

Dec 20, 2025 6 min read

A classic optimization problem proposed by Jose M.: What is the largest ellipse that fits inside a circle of radius $r$? By analyzing the tangency conditions of the curves, we derive the maximum area $A = \frac{2\sqrt{3}}{9}\pi r^2$.

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Number Theory Problem Solving

Summing Integer Square Roots: A Closed Formula

Dec 10, 2025 5 min read

Computing the sum $\sum_{k=1}^{n} \lfloor \sqrt{k} \rfloor$ term by term is inefficient for large $n$. In this post, we derive an elegant closed-form formula by regrouping the terms based on the intervals between consecutive perfect squares.

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