Final answer:
The equation for a line with an undefined slope passing through the point (0, -9) is x = 0.
Step-by-step explanation:
The equation of a line in the Cartesian coordinate system can be expressed in various forms, but one of the most common forms is the slope-intercept form.
The equation for a line with an undefined slope is x = a, where 'a' is a constant. In this case, the equation for the line with an undefined slope passing through the point (0, -9) is x = 0. This means that the line is a vertical line that intersects the x-axis at x = 0.