Given:
Slope is undefined.
To find:
Which graph has an undefined slope?
Solution:
We know that, slope is change in y-values with respect to x-values.
[tex]m=\dfrac{y_2-y_1}{x_2-x_1}[/tex]
The slope is undefined if the denominator is 0.
[tex]x_2-x_1=0[/tex]
[tex]x_2=x_1[/tex]
It means, the x-values are same. It is possible only for a vertical line.
Therefore, the slope of vertical lines are undefined or we can say that graph of a vertical line has an undefined slope. It is of the form [tex]x=a[/tex], where, a is a constant and it can be any real number.