What is the Coarea Formula and How Can It Be Proven?

[Matthollyw00d]

I'm trying to prove the coarea formula (not in the most general case) and it looks like it shouldn't be too difficult after an appropriate change of variable, however I'm not seeing that appropriate change of variable. Any hints? A link would work fine too, however outside the wikipedia page on coarea, I've yet to come across any site with anything relevant at all. For such an important formula, there sure is nothing on it.

 

[torquil]

Maybe section 4.2 here is relevant?:

http://arxiv.org/abs/0804.3291

Torquil

 

[Matthollyw00d]

I figured it out with a little integration over manifolds and fubini's theorem. Thanks anyway though.