
  Find the coefficients a, b, c, d of the circle,
       
       ax**2 + ay**2 + bx + cy + d  = 0 

        that passe through this three points.    
          
       (x[1],y[1])  (x[2],y[2])  (x[3],y[3])  

  Using the given points, we obtain this matrix.

  (a)x**2   (a)y**2   (b)x      (c)y        (d) = 0               

     x[1]**2   y[1]**2   x[1]      y[1]      1    0
     x[2]**2   y[2]**2   x[2]      y[2]      1    0
     x[3]**2   y[3]**2   x[3]      y[3]      1    0

  This system has three rows (3 points), and four values to find (a, b, c, d).
  If the system is consistent, it will have many solutions.

  To find one solution, I must give a value, to one of a coefficient.
  I have chosen to write a = 1.

  We obtain this matrix.

  (a)x**2   (a)y**2
              
     1         0         0         0         0    1  
     0         1         0         0         0    1 
     x[1]**2   y[1]**2   x[1]      y[1]      1    0 
     x[2]**2   y[2]**2   x[2]      y[2]      1    0 
     x[3]**2   y[3]**2   x[3]      y[3]      1    0 


  Now you can use gaussjordan() on the matrix,
  to find the value of a, b, c, d.
