yep. A vertical line is always undefined. My math teacher tried to run up a vertical wall several times and, of course, couldn't do it. That was his way of demonstrating that vertical = undefined.

so to sum it all up:

y=1 would be a horizontal line traveling through 1 on the y axis. 0 slope.

x=1 would be a vertical line traveling through 1 on the x axis. undefined.

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