Question 174418
Since {{{x=-1}}}, this means that EVERY point on the line has an x-coordinate of -1. So we have the points 



(-1,-2),(-1,-1),(-1,0),(-1,1),(-1,2)(-1,3), etc...



Notice how EVERY point has an x-coordinate of -1



Now let's plot the points



{{{drawing( 500, 500, -7, 7, -7, 7,
graph( 500, 500, -7, 7, -7, 7, 0),
circle(-1,-2,0.03),
circle(-1,-2,0.05),
circle(-1,-2,0.08),

circle(-1,-1,0.03),
circle(-1,-1,0.05),
circle(-1,-1,0.08),

circle(-1,0,0.03),
circle(-1,0,0.05),
circle(-1,0,0.08),

circle(-1,1,0.03),
circle(-1,1,0.05),
circle(-1,1,0.08),


circle(-1,2,0.03),
circle(-1,2,0.05),
circle(-1,2,0.08),


circle(-1,3,0.03),
circle(-1,3,0.05),
circle(-1,3,0.08)

)}}}




Now draw a line through the points



{{{drawing( 500, 500, -7, 7, -7, 7,
graph( 500, 500, -7, 7, -7, 7, 0),
blue(line(-1,-20,-1,20)),
circle(-1,-2,0.03),
circle(-1,-2,0.05),
circle(-1,-2,0.08),

circle(-1,-1,0.03),
circle(-1,-1,0.05),
circle(-1,-1,0.08),

circle(-1,0,0.03),
circle(-1,0,0.05),
circle(-1,0,0.08),

circle(-1,1,0.03),
circle(-1,1,0.05),
circle(-1,1,0.08),


circle(-1,2,0.03),
circle(-1,2,0.05),
circle(-1,2,0.08),


circle(-1,3,0.03),
circle(-1,3,0.05),
circle(-1,3,0.08)

)}}}



So we can see that the graph of {{{x=-1}}} is a vertical line.




Note: ANY equation in the form {{{x=k}}} where "k" is any number will graph a vertical line.