What Is Pi Day? Things To Know About The Holiday Celebrating An Iconic Mathematical Symbol

CBS San Francisco

March 14, 2024

Thursday marks National Pi Day in the United States and around the world. The holiday commemorates a timeless symbol beloved by many in mathematical and scientific communities, while making the most of the opportunities it allows for humorous wordplay, dessert and "teachable moments," as some experts have said.

Pi is a special number — so special, in fact, that most laypeople are probably aware of it, even if only as a relic of bygone classroom lectures or geometry textbooks. Represented in abbreviated form by the somewhat familiar sequence 3.14, pi, or the Greek letter π, is an iconic symbol seen in mathematical equations and, in more recent decades, merchandise like T-shirts, sweatshirts and coffee mugs.

It's actually a ratio, denoting the relationship between the circumference and the diameter of a circle. If the outline of a circle is traced, unwound and then measured, the length is called its circumference. The length of a line drawn straight through the center of a circle and extending out to its edges is called the diameter. Dividing the circumference by the diameter of any and all circles will yield the same result: pi — and that's true for all circles, regardless of size.

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