circle in 3d space?

Example of an equation of a circle in 3D:

x^2 + y^2 + z^2 = 81 and
5x - 4y + z + 3 =0

Since it can be transformed to a cicle in a 2D plane, just 3 points on the circle is enough to determine the centre as well as the radius.

e.g.
Given (1, 4, 8), (3, 6, 6), (4, 4, -7) on the above circle, by finding the intersection of the perpendicular bisectors(planes) of any two distinct line segments joining any two points and the plane contains the given 3 points, it can be found that the centre is (-5/14, 2/7, -1/14), and hence the radius is √(15834)/14.

3點連成一個三角形
任何三角形一定可以形成一個circle
只要用三條邊ge perpendicular bisector 就ok啦
第二條就可能唔得
但我唔識
幫你唔到