$\text{The slope of the line joining the points } (x_1,y_1) \text{ and } (x_2,y_2) \text{ is given by } m=\dfrac{y_2-y_1}{x_2-x_1}$.So, the slope of the line joining the points \(\left(8,-2\right)\) and \(\left(8,4\right)\) is \(\dfrac{\left(4\right)-\left(-2\right)}{\left(8\right)-\left(8\right)}\) = \(\dfrac{4+2}{8-8}\) = \(\dfrac{6}{0}\) = \(\infty\)The slope is not defined, so the line is vertical.