Question 518168
{{{ y = 4 }}} is not a vertical line.
It's a horizontal line.
That is, so long as you call the vertical
the y-axis, the way it usually is.
------------
The reason {{{ y=4 }}} is horizontal is
because (1) It wants to be {{{4}}} all
the time, no matter what, and (2)
It doesn't care what {{{x}}} is, so 
whether {{{ x = 5 }}} or {{{ x = 5000 }}}
doesn't matter.
The only line that satisfies these conditions 
is a horizontal line where every point
looks like (x,4)
Hope this helps