Problem involving del operator in vector analysis

[Sudip Maity]

Homework Statement

prove grad(f/g)=((g grad f)-(f grad g))/g^2,if g not equal to 0.

Homework Equations

no idea.

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.

 

[Phrak]

Use the definition of the del operator; otherwise you are just staring at upside-down triangles wondering what to do.

$$\nabla (f/g) = \frac{\partial (f/g)}{\partial x}i +\frac{\partial (f/g)}{\partial y}j + \frac{\partial(f/g)}{\partial z}k$$