Question 667949
  <pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
 line with an 'undefined' slope is a vertical Line
passing thu (-9/2,4)   x = -9/2

{{{drawing(300,300,   -6, 6, -6, 6,  blue(line(-4.5,6,-4.5,-6))  , grid(1),
circle(-4.5, 2,0.3),
circle(-4.5, -1,0.3),
graph( 300, 300, -6, 6, -6, 6))}}}