*f(r) is a scalar field, then use stoke's theorem (∫∫c curlF.d*

∫∫s grad(f) x d

**S**=∫cF.d**r**) to deduce that:∫∫s grad(f) x d

**S**= -∫c f d**r**I am stuck as to how to do this. I have tried subbing in the vector calculus identity curl(fu)=fcurl(u)+(gradf)xu (where u is a constant). Thus

∫∫s grad(f) x d

**S =**

*∫∫s*curl(fu) - fcurl(u) (where d

**S**is u)

but I am not sure whether this is right (and i then get stuck at this point too). Please help!