The Unit Circle
You just learned about The Circle Equation. If you didn't, then, i don't know. You shouldn't be reading this.
Let's take a circle of radius 1 that's centred on the origin, that is,
Basic geometry says you can always create a triangle inside this circle. We won't get into the geometry aspect of this, but this is probably all you need to know for a vague understanding of the origin of the next topic: