1. The problem statement, all variables and given/known data prove grad(f/g)=((g grad f)-(f grad g))/g^2,if g not equal to 0. 2. Relevant equations no idea. 3. The attempt at a solution rhs will be grad f -(f grad g)/g^2. can't make out what 2 do after that.referred other books but no help.it's a very obscure identity.found this in m.r.spiegel's vector analysis no.57 pg-78,chap GDC.