PPT Slide
if a line is vertical, it rises infinitely; its slope is undefined which we call “no slope”
these lines have equations which are in the form x = c where c is some real number. The coefficient of y is 0. There is no y-intercept except for the line x = 0, which is the equation for the y-axis.
Note that the change in x is 0. subtrcating a number from itself gives 0. This can’t be expressed as a fraction because you can’t divide by 0.