Hi, I posted a question some time ago and the suggestion was to use some form of the product rule but I still can't figure out what to do.(adsbygoogle = window.adsbygoogle || []).push({});

Q. Let f(x,y,z) and g(x,y,z) be C^2 scalar functions. Let D be an elementary region in space and [tex]\partial D[/tex] be the closed surface that bounds D. Prove that

[tex]\int\limits_{}^{} {\int\limits_{}^{} {\int\limits_D^{} {\nabla f \bullet \nabla g} dV = \int\limits_{}^{} {\int\limits_{\partial D}^{} {f\nabla g \bullet dS} - \int\limits_{}^{} {\int\limits_{}^{} {\int\limits_D^{} {f\nabla ^2 gdV} } } } } } [/tex]

Can someone give me a hint as to where to start, like any relevant identies which could be of use? Any help is appreciated thanks.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Multiple integrals

**Physics Forums | Science Articles, Homework Help, Discussion**