Slope(m)=(y2-y1)/(x2-x1) here (5,-9)=(x1,y1) (5,9)=(x2,y2) so, m= (9+9)/(5-5)=infinity it means the line is perpendicular with the x-axis because tan90 is equal to infinity so in order to make slope infinity the line should make 90 angle with positive x axis
