Given that for a function f(x,y),
df/dx = 2x + 7y and
df/dy = 7x + 9y
x(u,v) = cos v,
y(u,v) = ue^v
evaluate df/du and df/dv (in terms of u and v), using the following chain rule formulae:
df/du = (df/dx)(dx/du) + (df/dy)(dy/du)
and
df/dv = (df/dx)(dx/dv) + (df/dy)(dy/dv)