Chain Rule: Two and Three Independent Variables In Exercises 7 and 8, (a) express az/au and az/av as functions of u and v both by using the Chain Rule and by expressing z directly in terms of u and v before differentiating. Then (b) evaluate ǝz/au and az/av at the given point (u, v). 7. z = 4e In y, x = = (u, v) (2, π/4) In (u cos v), y = u sin v;