# 2 differential geometry questions

• May 6th 2013, 12:58 PM
Plato13
2 differential geometry questions
I need help with the the questions in the attachment. For the first I think I will have to use the regular value theorem for part of it. For the second, I need to use the theorem that f is a local isometry iff there is a basis e,e' of the tangent space such that df(e).df(e')=e.e', df(e).df(e)=e.e and df(e').df(e')=e'.e'. I want to find a basis by choosing a suitable co-ordinate chart for the domain. I'm a bit unsure how to deal with the fact that f is a function of rcos(theta) and rsin(theta) rather than r and theta.

Thanks
• May 6th 2013, 11:46 PM
chiro
Re: 2 differential geometry questions
Hey Plato13.

In terms of a basis, one suggestion I have (I don't know if it will be useful though) is to incorporate both constraints to eliminate one variable and then use a 3D polar parameterization for your object in part a.
• May 7th 2013, 04:59 AM
Plato13
Re: 2 differential geometry questions
Thanks, solved it now