Number 33, explain pls

In Exercises 23-34, find the critical points and apply the Second Deriva- tive Test (or state that it fails). 23. f (x) = x3 - 12x2+ 45x 24. f (x) - x4 - 8x2+ 1 25. f (x) = 3x4 - 8x3 + 6.x2 26. f (x) = x5 -x3 27. f (x) = x 2 - 8x 28. f (x) = x +1 x 2 - x +2 29. y = 6x3/2 - 4x1/2 30. y =9x7/3 - 21x1/2 31. f (x) = sin2 x + cosx, [0, x] 32. y = - sin x + 4' [0, 277 ] 33. f (x) = 2 + tan-x, (- 2)