International

# E-DAY - February 7

## E-DAY

Every year on February 7th, E-Day celebrates the mathematical constant e, which is also called Euler’s Number. It’s also a day to learn more about the Swiss mathematician, Leonhard Euler.

If you have ever taken an advanced math or physics course, you may recall seeing a little “e.” Though it’s a letter, it’s actually called Euler’s number. It has a mathematic value of 2.7182818. Like pi, the digits go on forever in a series that never repeats.

Euler’s number is usually used when trying to solve a formula or equation. One example of how Euler’s number is used is when trying to determine the rate of change. In biology, Euler’s number helps calculate the rate of exponential growth or decay. Population models are another application that Euler’s number is commonly used.

In finance, Euler’s number can also help calculate how compound interest causes wealth to grow. This is exactly how mathematician Jacob Bernoulli was using this number. In 1638, Bernoulli was trying to figure out how fast wealth would grow if it were compounded more than once a year.

Over 100 years later in 1748, Leonhard Euler began to work with this mathematical constant. It was Euler that proved it was an irrational number. While working with the constant, he used the letter “e” for the word “exponents”. However, the letter became commonly associated with his name. Euler is also known for founding the studies of graph theory and topology. He is considered one of the greatest mathematicians in history.

### HOW TO OBSERVE E-DAY

• Try to solve a formula or equation using the constant e.