(define (square x) (* x x))

(define (average x y)
  (/ (+ x y) 2))
  
(define (good-enough? guess x)
  (< (/ (abs (- (improve guess x) guess)) guess) 0.001))
  
(define (improve guess x)
  (/ 
   (+ (/ x (square guess)) (* 2 guess)) 
   3))

(define (cbrt-iter guess x)
  (if (good-enough? guess x)
      guess
      (cbrt-iter (improve guess x)
                 x)))

(define (my-cbrt x)
  (cbrt-iter 1.0 x))