*49*

No, this is not about the movie, but what is this famous number and how it came into our lives.

I really liked the movie, not for the outstanding script, but for the special effects and the colors captured in it. Anyway, maybe the ambition of that child, also. If you have a kid, it's a nice movie to watch. If you want more, I can recommend.

But now, let's go to our celebrated number.

Pi - it's the correspondent for the greek simbol - π - and it represents the ratio between the circumference and diameter of a circle, like the Euclidean definition stated.

Funny (and also sad) thing is that many mathematics teachers doesn't now the history of Pi or what it represents.

Besides Geometry, Pi has many areas of appliances. Look what Wikipedia says:

"The constant *π* (pi) has a natural definition in Euclidean geometry (the ratio between the circumference and diameter of a circle), but may be found in many places in mathematics: for example, the Gaussian integral in complex analysis, the roots of unity in number theory, and Cauchy distributions in probability. However, its ubiquity is not limited to pure mathematics. It appears in many formulas in physics, and several physical constants are most naturally defined with *π* or its reciprocal factored out. However, it is debatable whether such appearances are fundamental in any sense. For example, the textbook nonrelativistic ground state wave function of the hydrogen atom is

where a0 is the Bohr radius. This formula contains a *π*, but it is unclear if that is fundamental in a physical sense, or if it just reflects the *π* in the expression 4*π*r^2 (for the surface area of a sphere with radius r.

Furthermore, this formula gives only an approximate description of physical reality, as it omits spin, relativity, and the quantal nature of the electromagnetic field itself. Likewise, the appearance of *π* in the formula for Coulomb's law in SI units is dependent on that choice of units, and a historical accident having to do with how the so-called permittivity of free space was introduced into the practice of electromagnetism by Giovanni Giorgi in 1901. It is true that once various constants are chosen in one relation, the appearance of *π* in other relationships is unavoidable, but that appearance is always for a mathematical reason as in the example of the hydrogen atom wave function above, and not a physical one.

The numeric value of *π* is approximately 3.1415926536 (sequence A000796 in the OEIS). Memorizing increasingly precise digits of *π* is a world record pursuit."

You could see many things about *π, *and memorizing as long digits you can is a challenge for many (not for me, I cannot see this but a way to demonstrate something to someone).

A slide show brief history of Pi is presented here:

https://www.slideshare.net/pimath/history-of-pi

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We need to leave those geeks who tried to remember the most digits possible of this magic number and let's see **what is ***π ***good for***:*

*π*

Besides Geometry, where anything related to circles and not only are calculated using *π *, there are also other applications for real life, like how NASA is using it, from calculating a spacecraft trajectory to determining the diameter of a crater or operating robots.

"We use pi is used every single sol when operating Opportunity. Robots like radians, humans like degrees. Pi is our translator."

— Mike Seibert (@mikeseibert) March 14, 2014

https://www.universetoday.com/110331/happy-pi-day-5-ways-nasa-uses-pi/

Also, in fact, pi is needed for describing many things from the way light and sound waves ripple to the 'bendiness' of rivers, or calculating where circles are nowhere to be seen, such as Euler's Identity—a probability formula that has been described as the "most beautiful" in mathematics.

We have proverb in our country: " The wheel is spinning" - that means what now is up, could be sooner or later - down. And maybe if you can determine the size of the "wheel" in this case, you can calculate using *π *how long it could take until the fate is turning direction.

Of course, this is rather a philosophy, but it sounds nice.

Anyway, for any rational person of this world, this number should be celebrated because is no way of avoiding a meeting with it if you went to school. I first met it in the 6th grade. Long time ago, but I don't regret it. What are your memories from school about Geometry?

I'd like to hear about it. I can tell you I had only one teacher all the gymnasium period (this means 4 years - from 5th to 8th grade), but in high school I had 2. The first was severe, but fair and very good at teaching, the second was kind, but low at teaching.

Regarding this day, I will celebrate it by making a cookie with the symbol of *π *on it and I will eat it right away.

Cheers!

Or maybe, just for today - *πers!*