8. 9. z xy+y For a continuous function z = f(x,y) we found its derivative. x sin(xy)-x z - Use Clariault theorem (symmetry) to find; Use the Chain Rule to find w, and we where w = xyz and x=s+t and y=s-t and z = st z Use the Chain Rule to find where z = exy where x = t + s and y=t+s at (Express your answer in its simplest form in terms of the independent variables s and t)