We can calculate the slope of a line knowing two of the points of the line as:
In this case, we have x1 = x2. Then the slope m would result in a quotient with denominator 0, as (x2 - x1) = 0.
![m=(2-(-4))/(-4-(-4))=(6)/(0)=\text{undefined}]()
In this case, the only line that passes through (-4,-4) and (-4,2) is a vertical line with equation x = -4.
Vertical lines have undefined slope (they are not even function like f(x), as they have multiple values of y for the same value of x).
Then, as the slope is the rate of change of y for a unit change in x, is undefined for vertical lines.
Answer: undefined.