Question 732330
<pre>
That's correct, and that means it's a vertical line, which is "infinitely
steep", thus we say its slope is undefined.  Its equation is 

          x = 4,

because that's what is true about every point on that line.  Every point 
on that vertical line has an x coordinate of 4, like the two given points have,
(4, 8) and (4, -11).

{{{drawing(400,540,-10,10,-15,12,graph(400,540,-10,10,-15,12), 
circle(4,8,.2), circle(4,-11,.2), locate(4,8,"(4,8)"), locate(4,-11,"(4,-11)"),
green(line(4,-20,4,20)))}}}

Edwin</pre>