How to find B coordinates when A, C coordinates are known?

Question

JavaScript

https://codepen.io/kapysta-xxl/pen/eYyMNzy

I will be glad to any answer, even the same formula.
I don’t understand how to find coordinates at all, since there are both negative and positive

Answer 1

If only points A, C are given - point B can be positioned as you like - they define a quadratic Bezier curve in three. Look at the examples - your case is the second. The points can be moved.

Answer 2

information is not enough
knowledge is needed, for example, how is the green line located or what exactly (formula) is the blue one? or at least the angle between the red