# How do you find the slope of the line x=9?

Slope$=$indeterminate.
To try to evaluate it you can use the definition of slope $m$:
$m = \frac{\Delta y}{\Delta x}$ but your equation for any $y$ will always have $x = 9$ so $\Delta x = 0$!!!!
The relationship for the slope $m = \frac{\Delta y}{\Delta x}$ will then give you a division by zero, which is ideterminate.