#| BEGIN (Write your solution here) |#
(define (cube-root x)
  (cbrt-iter 1.0 x))

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

(define (improve guess x)
  (/ (+ (/ x (* guess guess)) (* 2 guess)) 
     3))

(define (good-enough? guess x) 
  (< (/ (abs (- (improve guess x) guess)) guess) 
     0.000000001))

#| END |#