What do you know about the slope when X2 - X1 = 0?

slope is undefined

Step-by-step explanation:

Using the slope formula

m = (y₂ - y₁) / (x₂ - x₁)

If x₂ - x₁ = 0

Since division by zero is undefined then the slope of the line is undefined

This applies to a vertical line parallel to the y - axis