Having a bit of a problem with this partial derivative, i know how to do the problem if the x and y wasn't infront as you could apply the product rule and apply the partial derivative, however having problems in what to do with it, here is the problem:

f(x,y)=xcosx*coshy+ysinx*sinhy

Determine partial df/dx, df/dy, second partial df/dx, second partial df/dy and partial d^2f/dxdy

Many thanks in advance.