Problem with partial derivatives

[ak123456]

Homework Statement

suppose that f(x,y)=f(y,x) for all (x,y)\inR^2 show that
(for partial derivative )
Df/Dx (a,b)=Df/Dy(b,a)

Homework Equations

The Attempt at a Solution

i don't know how to start
can i do like this
set g(x,y)=f(y,x)
f o g (x,y) =f(x,y)
then how to continue ?

 

[Mark44]

Since you don't have much to go on, I'd suggest that you use the definition of the partial derivative for each of the two partials.