SICP 問題 2.12
(define (make-center-width c w) (make-interval (- c w) (+ c w))) (define (center i) (/ (+ (lower-bound i) (upper-bound i)) 2)) (define (width i) (/ (- (upper-bound i) (lower-bound i)) 2)) (define (make-center-percent c p) (make-interval c (* c (/ w 100)))) (define (percent i) (* (/ (width i) (center i)) 100))