Your explanation is correct, but there are some suggestions to make it less wordy and redundant:
The formula for determining the slope using two points, m = (y2 - y1) / (x2 - x1), cannot be used for vertical lines because it involves dividing by zero, which is undefined. The formula requires two distinct points to calculate the change in y divided by the change in x.
Vertical lines, on the other hand, have the equation x = some number (e.g., x = 6). These lines have an undefined slope because any two points on a vertical line will have the same x-coordinate. Therefore, the change in x is always zero, resulting in a division by zero when attempting to evaluate the slope. Hence, the concept of slope simply does not apply to vertical lines.
To summarize, the formula for determining slope using two points is not applicable to vertical lines because dividing by zero is undefined, and the change in x for vertical lines is always zero.