Number π

The ratio of circum­fer­ence length to its diam­eter does not depend on its size – i.e., is a fixed number. This number is denoted with the π letter in math­e­matics.

The number π can be written as an infi­nite non-peri­odic decimal number $$ \pi=3,1415926535… $$

The fact that it equals “three and change” can be demon­strated with use of a cork tea mat, rope and two pins.

Wind the rope around the mat lying on the table and cut the rope so that it had the same length as the circum­fer­ence.

Sticking the pins in two diamet­ri­cally oppo­site points, one can demon­strate that this rope would now make three folds along the diam­eter, leaving some “change”.

The struggle for finding the most precise value of this “change” was exciting and took centuries.

One π’s prop­er­ties is that you could find your birthday date after the dot in its decimal form.