2.10.rkt

#lang scheme
; 预定义函数
(define (make-interval a b) (cons a b))
(define (lower-bound z)
  (min (car z)
       (cdr z)))
(define (upper-bound z)
  (max (car z)
       (cdr z)))
(define (mul-interval x y)
  (let ((p1 (* (lower-bound x) (lower-bound y)))
        (p2 (* (lower-bound x) (upper-bound y)))
        (p3 (* (upper-bound x) (lower-bound y)))
        (p4 (* (upper-bound x) (upper-bound y))))
    (make-interval (min p1 p2 p3 p4)
                   (max p1 p2 p3 p4))))
; 修改除法运算
(define (div-interval x y)
  (let ((y-max (upper-bound y))
        (y-min (lower-bound y)))
    (if (< (* y-max y-min) 0)
        (display "不能除以含0区间")
        (mul-interval x  
                      (make-interval (/ 1.0 y-max) 
                                     (/ 1.0 y-min))))))