; calculating derivatives

(define dx 0.0000001)

(define (deriv f)
  (define (f-prime x)
    (/ (- (f (+ x dx)) (f x))
       dx))
  f-prime)

(define (cube x) (* x x x))

(display ((deriv cube) 2)) (newline)
(display ((deriv cube) 3)) (newline)
(display ((deriv cube) 4)) (newline)