\pi day is celebrated every year on March 14 because \pi \approx 3.14.
If we draw a circle of radius 1, then \pi is the length of a semicircle.
The length of the whole circle is denoted by \tau, thus, \tau = 2 \pi \approx 6.28
In the figure below, the perimeter of the hexagon is 6, so the circumference of the circle is a little bit greater than 6:
\tau > \approx 6
so \pi is a tiny bit bigger than 3:
\pi > \approx 3
To celebrate this year's \pi day, let us enjoy this beautiful identity about \pi due to the mathematician Euler:
\frac{1}{1^2} + \frac{1}{2^2} + \frac{1}{3^2} + \frac{1}{4^2} + \frac{1}{5^2} + \dots = \frac{\pi^2}{6}
Happy \pi day everyone!!!
