Answer
See below.
Work Step by Step
We know that by the Slope Formula: if $P_1(x_1,y_1)$ and $P_2(x_2,y_2)$ are on a line, then the slope is: $m=\frac{y_2-y_1}{x_2-x_1}$.
Hence here: $m=\frac{-1-2}{3-3}=\frac{-3}{0}.$ Division with $0$ is undefined, thus the slope is undefined, thus the line is vertical.
