# Happy Pythagorean Theorem Day 2020

For the first time since 2017, December 16, 2020 marks another Pythagorean Theorem Day!

The square of the hypotenuse of a right triangle is equal to the sum of the squares of the two adjacent sides.

My fellow mathematicians and math enthusiasts, let’s celebrate! For the first time since 2017, we’ve come upon another Pythagorean Theorem Day. (And here we thought 2020 wouldn’t bring us anything good at all!)

A quick history lesson:
Many historians believe that the Pythagorean Theorem itself was discovered many times over by mathematicians and philosophers across the "sands of time". While it is named after the Greek philosopher Pythagoras (570-495 BCE), its earliest records were found inscribed upon Babylonian tablets, dating back to roughly 2000-1600 BCE - more than a thousand years before Pythagoras was even born! The theorem was also independently discovered by both Indian and Chinese mathematicians. It can be found mentioned in the Baudhayana Sulba-sutra of India (800-400 BCE), and recorded within The Nine Chapters on the Mathematical Art of China (produced during the Han Dynasty, 202 BCE - 220 AD).

...now back to the celebration!
This special math holiday is celebrated when the sum of the squares of the month and day are equal to the square of the year. Let’s see how this works out for December 16th, 2020:

Pretty cool, huh?

The last time we celebrated Pythagorean Theorem Day was back in August 15, 2017.

If you're like anyone on the Mathspace team, your curiosity has been ignited and are probably wondering, "So, what other dates fit perfectly into the Pythagorean Theorem?" Well, our team put together this fantastic GeoGebra applet that runs through all of the dates since 2001, calculates the sum of the square of the month and the day, and checks to see if it equals the square of the year.

This decade will give us two more of these Pythagorean holidays - July 24, 2025 and October 24, 2026. But if you miss the chance to celebrate them, you'll be waiting until March 4, 2105 to join in the math fun. (That is, if medicine and technology allows us to live that long!)

So in the meantime, let's pull out the party hats and add this year's Pythagorean Theorem Day to our holiday festivities. Enjoy!