I have read the book, tried looking at similar examples, but I simply cannot solve the following problem:

The function f(u,v) is differentiable in the entire R^2. Write:

h(x,y,z)= f(x/y, y/z)

y>0, z> 0

(do not understand why this is of importance)

Calculate:

x*(dh/dx)+y*(dh/dy)+z*(dh/dz) expressed in u, v and partial derivates of f.

The dh/dx, dh/dy and dh/dz all have those crooked d's which I cannot type here.

I really need help with this and would be so thankful for any guidance!