Best Mathematical Equations

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I believe most people would give top marks to Euler's Identity as the most beautiful mathematical equation as it ties into one, simple equation, five key mathematical constants (unity, Pi, zero, e, and i). Recently, Scientific America, published an article listing several more beautiful mathematical equations: https://www.scientificamerican.com/article/these-are-the-most-beautiful-equations-in-mathematics/. Of these, I like Euler's Product as a very close second place.

Update: July 6, 2024: IFL Science recently published a list of the three most important equations: https://www.iflscience.com/three-incredible-equations-and-why-theyre-so-important-74961