Question 91101
Since x=4, our x values will always be x=4. So the only thing that will change is the y-value. Lets plot some points for the equation x=4







Plot the point in (4,-5) (note: we can start at any y value)




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05)
)}}}





Now add the point in (4,-4):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05)
)}}}





Now add the point in (4,-3):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05),
circle(4,-3,0.05),
circle(4,-3,0.05)
)}}}





Now add the point in (4,-2):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05),
circle(4,-3,0.05),
circle(4,-3,0.05),
circle(4,-2,0.05),
circle(4,-2,0.05)
)}}}





Now add the point in (4,-1):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05),
circle(4,-3,0.05),
circle(4,-3,0.05),
circle(4,-2,0.05),
circle(4,-2,0.05),
circle(4,-1,0.05),
circle(4,-1,0.05)
)}}}





Now add the point in (4,0):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05),
circle(4,-3,0.05),
circle(4,-3,0.05),
circle(4,-2,0.05),
circle(4,-2,0.05),
circle(4,-1,0.05),
circle(4,-1,0.05),
circle(4,0,0.05),
circle(4,0,0.05)
)}}}





Now add the point in (4,1):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05),
circle(4,-3,0.05),
circle(4,-3,0.05),
circle(4,-2,0.05),
circle(4,-2,0.05),
circle(4,-1,0.05),
circle(4,-1,0.05),
circle(4,0,0.05),
circle(4,0,0.05),
circle(4,1,0.05),
circle(4,1,0.05)
)}}}





Now add the point in (4,2):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05),
circle(4,-3,0.05),
circle(4,-3,0.05),
circle(4,-2,0.05),
circle(4,-2,0.05),
circle(4,-1,0.05),
circle(4,-1,0.05),
circle(4,0,0.05),
circle(4,0,0.05),
circle(4,1,0.05),
circle(4,1,0.05),
circle(4,2,0.05),
circle(4,2,0.05)
)}}}





Now add the point in (4,3):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05),
circle(4,-3,0.05),
circle(4,-3,0.05),
circle(4,-2,0.05),
circle(4,-2,0.05),
circle(4,-1,0.05),
circle(4,-1,0.05),
circle(4,0,0.05),
circle(4,0,0.05),
circle(4,1,0.05),
circle(4,1,0.05),
circle(4,2,0.05),
circle(4,2,0.05),
circle(4,3,0.05),
circle(4,3,0.05)
)}}}





Now add the point in (4,4):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05),
circle(4,-3,0.05),
circle(4,-3,0.05),
circle(4,-2,0.05),
circle(4,-2,0.05),
circle(4,-1,0.05),
circle(4,-1,0.05),
circle(4,0,0.05),
circle(4,0,0.05),
circle(4,1,0.05),
circle(4,1,0.05),
circle(4,2,0.05),
circle(4,2,0.05),
circle(4,3,0.05),
circle(4,3,0.05),
circle(4,4,0.05),
circle(4,4,0.05)
)}}}





Now add the point in (4,5):




{{{drawing(500,500,-5,5,-5,5,
grid( 1 ),
circle(4,-5,0.05),
circle(4,-5,0.05),
circle(4,-4,0.05),
circle(4,-4,0.05),
circle(4,-3,0.05),
circle(4,-3,0.05),
circle(4,-2,0.05),
circle(4,-2,0.05),
circle(4,-1,0.05),
circle(4,-1,0.05),
circle(4,0,0.05),
circle(4,0,0.05),
circle(4,1,0.05),
circle(4,1,0.05),
circle(4,2,0.05),
circle(4,2,0.05),
circle(4,3,0.05),
circle(4,3,0.05),
circle(4,4,0.05),
circle(4,4,0.05),
circle(4,5,0.05),
circle(4,5,0.05)
)}}}







We can see that the points form a vertical line. So that means x=4 is a vertical line through x=4


As a general rule, any equation {{{x=n}}} is a vertical line through x=n