ELI5: Explain Like I'm 5

Fay's trisecant identity

Okay kiddo, have you ever drawn a circle on a piece of paper? Fay's trisecant identity is about that circle!

We know that the circle is made up of infinite points all around it. Now, let's say we pick three of these points and draw straight lines connecting them. These lines are called secants.

But what if we made three more points on the circle, equally spaced between the first three points? These new points will also be connected by straight lines to form new secants.

Now, Fay's trisecant identity tells us that if we multiply the lengths of the first three secants together, and then multiply the lengths of the next three secants together, and then add those two products together, we will get a certain value.

This value is equal to the product of the lengths of the first three secants again, but this time multiplied by a special fraction that has to do with the distance between each set of three points.

It might be hard to understand exactly why this is important or how it's used in math, but just remember that it helps us understand circles better and figure out some cool things about them!