ป.ร. ให้ไว้ # การ y = f (x) #, # f '(x) = lim_ (hto0) (f (x + H) -f (x)) / H #
# f '(x) = lim_ (hto0) (tanh (x + H) -tan (x)) / H #
# f '(x) = lim_ (hto0) ((tanh (x) + tanh (H)) / (1 + tanh (x) tanh (H)) - ผิวสีแทน (x)) / H #
# f '(x) = lim_ (hto0) ((tanh (x) + tanh (H)) / (1 + tanh (x) tanh (H)) - (tanh (x) + tanh (H) tanh ^ 2 (x)) / (1 + tanh (x) tanh (h))) / เอช #
# f '(x) = lim_ (hto0) ((tanh (x) + tanh (H) -tanh (x) -tanh (H) tanh ^ 2 (x)) / (1 + tanh (x) tanh (h))) / เอช #
# f '(x) = lim_ (hto0) (tanh (x) + tanh (H) -tanh (x) -tanh (H) tanh ^ 2 (x)) / (h (1 + tanh (x) tanh (เอช))) #
# f '(x) = lim_ (hto0) (tanh (H) -tanh (H) tanh ^ 2 (x)) / (h (1 + tanh (x) tanh (h))) #
# f '(x) = lim_ (hto0) (tanh (H) (1-tanh ^ 2 (x))) / (h (1 + tanh (x) tanh (h))) #
# f '(x) = lim_ (hto0) (tanh (H) sech ^ 2 (x)) / (h (1 + tanh (x) tanh (h))) #
# f '(x) = lim_ (hto0) (Sinh (H) sech ^ 2 (x)) / (hcosh (H) (1 + tanh (x) tanh (h))) #
# f '(x) = lim_ (hto0) Sinh (H) / ชั่วโมง * lim_ (hto0) sech ^ 2 (x) / (กระบอง (H) (1 + tanh (x) tanh (h))) #
# f (x) = 1 * sech ^ 2 (x) / (กระบอง (0) (1 + tanh (x) tanh (0))) #
# f (x) = 1 * sech ^ 2 (x) / (1 (1 + 0)) #
# f '(x) = sech ^ 2 (x) #
