To find the slope of a line, we use the formula for slope (m), which is defined as the change in y divided by the change in x. In this case, when y is constant at 15, it means we have a horizontal line.
1. **Understanding the scenario**: Since y = 15, this line does not change vertically, regardless of the value of x. Thus, it is a horizontal line.
2. **Calculate the slope**: The slope of a horizontal line is always 0. This is because there is no vertical change (Δy = 0) as we move along the x-axis, which means:
m = Δy / Δx = 0 / (any non-zero number) = 0
3. **Slope for x = 9**: When we mention the slope of x = 9, it typically refers to a vertical line at x = 9. For a vertical line, the slope is undefined because the change in x (Δx) is 0 while we have a vertical change (Δy).
In summary:
- For the line where y = 15, the slope is 0.
- For the line where x = 9, the slope is undefined.