i have to show that dy/dx= (x+y)/(x-y) if arctan (y/x)= log(sq.rt.(x^2 + y^2))

i was able to get everything before this, but i dont really understand what the questions asking. also, i just did a whole page of tanh x, so that keeps interfering with my memory of arctan.

any help would be very appreciative, thanks alot!