The point-slope form of the equation of a line is given as per below;

where m = slope.
Let's go ahead and find the slope of the line using the below equation;

From the question, we know that x1 = 5, x2 = 5, y1 = -9 and y2 = 8.
So let's substitute these values into the above equation and find the slope;
![\begin{gathered} m=(8-(-9))/(5-5) \\ m=(8+9)/(0) \\ m=(17)/(0) \\ \therefore m=\text{undefined} \end{gathered}]()
We can see that the slope of the line is undefined. So it means that the line is a vertical line because x2-x1 = 0.
Our equation will now be y = -9
NB: Vertical lines always have undefined slope while horizontal lines always have their slope to be equal to zero.