- #1

trickycheese1

- 5

- 0

## Homework Statement

Prove the following or disprove with a counterexample: Let f be a differentiable function in an open set U in R^3 and (a, b, c) be a point in U where the gradient of the function f isn't zero. If r: I -> U is a regular curve with a regular derivative on an open interval I, which contains the zero point, and satisfies the following conditions:

r(0) = (a, b, c)

r(I) is contained in the contour surface of the function f that goes through the point (a, b, c)

## Homework Equations

The osculating plane is given with {r(0) + a*r'(0) + b*r''(0) : a, b are reals}.

## The Attempt at a Solution

Since r is regular with with a regular derivative then r' dot r'' = 0. Since r is contained in the contour surface then gradient(f) dot r' = 0. If I can show that the gradient of f dot r'' is or isn't 0 then this is done. I can't find any relevant theorems for this problem though.