Tangents and distance formula

[Niall]

The tangent P(3,9) on the curve y = x^2, cuts the x-axis at T and PN is perpendicular to the x-axis. Find the length of TN.

So far I have:

dy/dx = 2x
dy/dx = 6

y - 9 = 6(x - 3)
y = 6x - 9

Making point T (3/2, 0), but how do you find point N?

Thank you.

 

[ZaidAlyafey]

We have got that PN is perpendicular to the x-axis what do we conclude ?