Why the slope of any vertical line is undefined?

Any vertical line is parallel to the y-axis in a co-ordinate plane.

Therefore the angle of inclination is equal to 90 degrees.

According to the formula , slope of a line = tanΘ

Θ = 90.

Therefore slope = tan 90

= sq.rt of {0/(4-4)}

= sq.rt of 0/0

= 0/0

= undefined.