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;;; Under Creative Commons Attribution-ShareAlike 4.0
;;; International. See
;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
(define-module (one eight)
#:export (cube double
div-three improve
good-enough? cbrt-iter
cbrt-sicp))
(use-modules (one six))
(define (cube x)
(* (square x) x))
(define (double x)
(* 2 x))
(define (div-three x)
(/ x 3.0))
(define (improve y x)
(div-three (+ (/ x (square y))
(double y))))
(define (good-enough? y x)
(< (abs (- (cube y) x))
0.001))
(define (cbrt-iter y x)
(if (good-enough? y x)
y
(cbrt-iter (improve y x)
x)))
(define (cbrt-sicp x)
(cbrt-iter 1.0 x))
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