Well, it’s almost Pi (π) Day again! And once more, we find reasons to celebrate that most interesting number on March 14. Most of us remember that π is the ratio of a circle’s circumference to its diameter. And some of us even remember that it is an irrational number – that is, it cannot be represented as a simple fraction and the decimal fraction goes on forever without repeating. We can approximate its value with arbitrary precision – a couple of years ago one enthusiast calculated more than 22 trillion decimal places. In theory (if π is a “normal” number, as appears likely, though unproven) any string of numbers you can think of will appear somewhere in those digits: your birthday, your social security number, even your bank account number.
One of the reasons π is so intriguing is that it keeps showing up almost everywhere we look. And its uses range from answering practical everyday questions to exploring the deepest mysteries of the universe. Below, we share some ways in which π is used.
Everyday uses include formulas for circles and spheres (and some useful shortcuts). If you take the value of π as 3 and the radius equal to d/2, those intimidating formulas we all learned for circumference, area and volume become quite simple and are still accurate to better than 5%.
Try them on these everyday questions:
Now we get a little more obscure: