CTK Exchange . What makes the points on the line numbers is that you can add and multiply them. That is why I don't understand what unreal numbers are. Every point in the plane is interpreted as a complex number the moment you define operations of addition and multiplication.
Vectors have a length which is a real nonnegative number.
The length of a complex number is its distance from the origin or the length of the corresponding line segment. The fourth vertex is the sum of the two numbers. Given two complex numbers. Let L be the product of their lengths. Let A be the sum of their angles.