S = (y2-y1) / (x2-x1)
S = (7 - 3) / (-4 - -4)
S = 4 / 0
S = 0
or you can just note how both x points are the same, so it must be a straight, vertical line
if both x points are the same, it's a vertical line that passes through (that point, 0)
if both y points are the same, it's a horizontal line that passes through (0, that point)
the slope of a line that's parallel to either is going to have the same slope because they will never intersect, therefore proving that they never bend or are at different angles
