# Differential geometry

1. Jul 19, 2007

### daishin

1. The problem statement, all variables and given/known data
On R^3 with the usual coordinates (x,y,z), consider the pairs of vector fields X,Y given below. For each pair, determine if there is a function f:R^3-->R with non-vanishing derivative df satisfying Xf=Yf=0, and either find such a function or prove that there is none.
(a) X=(e^x)d/dx - ((e^x)z + 2y)d/dz, Y=(e^x)d/dy - (2y)d/dz
(b) X=(e^x)d/dx - ((e^x)z + 2x)d/dz, Y=(e^x)d/dy - (2y)d/dz
2. Relevant equations

Could you help me start this problem.

3. The attempt at a solution

Sorry I don't know how to start this problem.

2. Jul 19, 2007

### Dick

You'll want to start by looking up Frobenius integrability conditions.

3. Jul 24, 2007

### daishin

More hint or idea.

OK I looked at Frobenius integrability condition and still have no clue.
How can I use the integrability condition??

4. Jul 24, 2007

### Dick

What is the integrability condition stated in terms of vector fields? You are talking about stuff I haven't looked at for a long time, but isn't the existence of a solution to the PDE's corresponding to these vector fields related to the commutator of the vector fields?

5. Jul 24, 2007

### daishin

Frobenius' Theorem

Yes. A distribution D={E(x)} on a manifold M is integrable iff for all vector fiels V,W on M with V(x),W(x) in E(x) for all x in M, [v,w](x) in E(x) for all x in M. But how can I relate this with the problem I asked?