# The n-sphere and the n-dimensional projective plane are locally isometric

1. Nov 1, 2008

### InbredDummy

1. The problem statement, all variables and given/known data
Prove that $$S^n$$ and $$P^n(R)$$ are locally isometric.

2. Relevant equations
So I proved that the antipodal mapping A(p) = -p is an isometry. And I proved that the projection map from $$S^n$$ to $$P^n(R)$$ is a local diffeomorphism. I'm just not sure what the Riemannian metric on $$P^n(R)$$ would be.

3. The attempt at a solution

I think it should be easy once I have the previous two facts, but can anyone help me just put it all together?

Thanks guys

2. Nov 7, 2008

### InbredDummy

EDIT: I got it! I finally got it!

Last edited: Nov 7, 2008
3. Nov 7, 2008

### Dick

Good! I was going to suggest the metric in the projective plane must be the one that it gets from the sphere, since they didn't give it to you. That would make it trivial. Is it that simple? Or am I just being simple minded?