Question 64011
I think that "slope undefined" means that slope = infinity.
I've seen it expressed this way. If they didn't give you 
information about the slope, they probably would say
"slope not given" or something like that.
If the slope is infinite, it a vertical line through
the given point. x = constant defines a vertical line
where the constant is the x-coordinate of the point
that it goes through, in this case, (1,2)
So, x = 1 is the equation of the line.