Final Answer:
The slope of the line passing through the points (-10,9) and (-10,18) is undefined.
Step-by-step explanation:
To determine the slope of a line using two points, the slope formula
is employed. For the given points (-10,9) and (-10,18), the formula is applied:

Simplifying the calculation:

The denominator of zero arises when the x-values of both points are identical. This scenario indicates a vertical line. In geometry, a vertical line's slope is undefined because it doesn't follow the traditional slope pattern of rise over run. Instead, it ascends or descends vertically without a horizontal shift. When x-values are equal but y-values differ, as in this case (-10,9) and (-10,18), it signifies a line that's parallel to the y-axis, hence perfectly vertical. Due to this vertical orientation, the slope is undefined.
Therefore, the line passing through the points (-10,9) and (-10,18) is vertical, and as a result, its slope is undefined in the context of traditional slope calculations.