#lang racket ; draw a graph of cos and deriv^3(cos)
(require plot)
(define ((deriv f) x)
  (/ (- (f x) (f (- x 0.001))) 0.001))
(define (thrice f) (lambda (x) (f (f (f x)))))
(plot (mix (line ((thrice deriv) sin) #:color 'red)
           (line cos #:color 'blue)))