see if you can answer this one

Let f = f(u,v) and u = x + y, v = x - y

i) assume f to be twice differentiable and compute f_{xx} and f_{yy} in terms of f_{u}, f_{v}, f_{uu}, f_{uv} and f_{vv}.

ii)express the wave equation:

((∂²f)/(∂x²))-((∂²f)/(∂y²))=0

in terms of partial derivatives of f with respect to u and v.