In Exercises 21-42, find the derivative of y with respect to the appro-priate variable.
21. $y = \cos^{-1}(x^2)$
22. $y = \cos^{-1}(1/x)$
23. $y = \sin^{-1}\sqrt{2}t$
24. $y = \sin^{-1}(1 - t)$
25. $y = \sec^{-1}(2s + 1)$
26. $y = \sec^{-1}5s$
27. $y = \csc^{-1}(x^2 + 1), x > 0$
28. $y = \csc^{-1}\frac{x}{2}$