## first year uni math problem~~

if w=f(u,v)has continuous partial derivatives and u=x+y
and v=x-y,use the chain rule to show that

(dw/dx)/(dw/dy)=(df/du)^2-(df/dv)^2

this is a first year uni math problem,is there anyone can help we with it??
thx a lot!
 PhysOrg.com science news on PhysOrg.com >> King Richard III found in 'untidy lozenge-shaped grave'>> Google Drive sports new view and scan enhancements>> Researcher admits mistakes in stem cell study
 do you know the chain rule?
 yeah i know,but no idea hw do i apply on this question~~

## first year uni math problem~~

$$\frac{\partial w}{\partial x} = \frac{\partial f}{\partial u} \frac{\partial u}{\partial x} + \frac{\partial f}{\partial v} \frac{\partial v}{\partial x}$$

$$\frac{\partial w}{\partial y} = \frac{\partial f}{\partial u} \frac{\partial u}{\partial y} + \frac{\partial f}{\partial v} \frac{\partial v}{\partial y}$$
 ok,i got it,but i still not clear which varible i take respect to when i differenciate for u=x+y and v=x-y....
 $$\frac{\partial w}{\partial x} = \frac{\partial f}{\partial u} \frac{\partial u}{\partial x} + \frac{\partial f}{\partial v} \frac{\partial v}{\partial x} = \frac{\partial f}{\partial u}*1 + \frac{\partial f}{\partial v}*1 = \frac{\partial f}{\partial u} + \frac{\partial f}{\partial v}$$
 oh!!!!i got it~~~ thx mates~