ELI5: Explain Like I'm 5

Barycentric coordinate system (mathematics)

Okay, so imagine you and your two friends are standing in a triangle, and you want to describe where you are in that triangle. Normally, you might say "I'm on this side or that side," or "I'm in the middle or on the corner." But if you want to be really specific, you could use barycentric coordinates.

Barycentric coordinates are like a special way of labeling points inside a triangle. Instead of using the usual x-y coordinates (like on a map), barycentric coordinates tell you how much of each corner you're closest to. So if you're closer to one corner than the others, your barycentric coordinate for that corner will be higher.

Here's how it works. You pick one of the corners of the triangle and call it "A." Then you draw a line from A to where you are standing, and you measure how long that line is. That's your first barycentric coordinate. Let's call it "a."

Next, you do the same thing for the second corner, which we'll call "B." You draw a line from B to where you are standing, and you measure how long that line is. That's your second barycentric coordinate, which we'll call "b."

Finally, you do the same thing for the third corner, which we'll call "C." You draw a line from C to where you are standing, and you measure how long that line is. That's your third barycentric coordinate, which we'll call "c."

Now you have three numbers: a, b, and c. Together, they tell you exactly where you are inside the triangle! If you're right in the middle of the triangle, all of your barycentric coordinates will be the same – for example, (1/3, 1/3, 1/3). But if you're closer to one corner than the others, that one coordinate will be higher than the other two.

So why would anyone use barycentric coordinates instead of regular x-y coordinates? Well, for one thing, they make it really easy to describe things that happen inside the triangle. For example, if you want to find the midpoint between two points inside the triangle, you can just take the average of their barycentric coordinates! Plus, barycentric coordinates work well with certain math problems that involve triangles, like finding perpendicular bisectors or circumcenters.

Overall, barycentric coordinates might seem confusing at first, but they're actually a handy tool for describing points inside a triangle in a really precise way.