In[4]:=
  { D[x Log[y] + z Log[x],x],
    D[x Log[y] + z Log[x],y],
     D[x Log[y] + z Log[x],z]}

Out[4]=

   z           x
  {- + Log[y], -, Log[x]}
   x           y

Up to 2 (4 points). a) Compute the gradient vector field of the function f(x,y,z) = x ln(y) + z ln(x).