Please do question 19 and 22

18. u = e'8(e2 + es, Int, In(etts + 1)). In Exercises 19 through 22, obtain a formula for the partial derivatives indicated. (Assume that the first variable of f is x and the second is y.) au du du 19. u = f(tr, ts); at' ar' as au du du 20. u = f(tx, ty); at ' ax' dy (Note: Here we are allowing x and y to stand not only for the variables of f, but we are also letting them appear in the formula.) du du 21. u = f(-x, - y) ; ax' dy au du 22. u = f(y, x); ax' ay In Exercises 23 through 26. use the ch