When trying to navigate to the Bezier Curve documentation, I get a 404 error in response. I do not know if this was intentional or if the page was accidently deleted. This link is present on several forum posts. I have listed some of those posts below:
So at one point, the page did exist. Since both quadratic and cubic Bezier Curves are used frequently in graphics work (game especially), one would assume that Roblox would have documentation on it.
Page URL: https://create.roblox.com/docs/mechanics/bezier-curves