**Curve tangent and normal**

You have to determine the unit vectors normal to the path.

Set a function as, phi = x^^2 - 2by

Now grad(phi) = d(phi)/dx**i** + d(phi)/dy**j**

Then, **n** = grad (phi)/ |grad(phi)|

and for **t**, swap the **n** coefficients *i* and **j**.

Goes something like that....