SICP Exercise 1.8

gistfile1.scm

;; SICP 1.8
;; Fork me. Solve me.

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

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

(define (good-enough? guess x)
  (< (abs (- (cube guess) x)) 0.001))

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