SICP Exercise 1.8

Exercise1-8.scm

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

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

(define (good-enough? guess prev-guess)
  (< (abs (- guess prev-guess)) 0.001))
; good-enough?

(define (cbrt x)
  (cbrt-iter 1.0 0.0 x))
; cbrt

; Test cases:-
(cbrt 0.000001)
; 1.0039485733107844e-2
(cbrt 1e15)
; 10000.