G.MATH
VECTOR DIFFERENTIAL CALCULUS
The Frenet-Serret formulas

We will now round up our discussion on the three unit vectors - the unit tangent, the unit normal and the unit binormal by deriving certain formulas involving the first derivatives of each vector.

These formulas are called the Frenet-Serret formulas.
VIDEO LECTURE


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CONCEPT
Recall our previous results, that is

 and

It seems logical first that we find the first derivative of the unit normal  with respect to arc length . To get that, we simply represent  in its cross product and differentiate accordingly, and employing substitution with the previous equations.

Together the three formulas are

And so I present to you The Frenet-Serret formulas which are of fundamental importance in the theory of curve in 3-space. These formulas can also be represented in matrix form as:

We shall see very soon how a curve can be solely described by the functions of curvature  and torsion  leading up to the fundamental theorem of space curves. This will get quite exciting!

All information presentated, less questions and exercises, is original content of Donny, with slight references to various books.
Video courtesy of YouTube.com service.
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