;; The first three lines of this file were inserted by DrScheme. They record metadata ;; about the language level of this file in a form that our tools can easily process. #reader(lib "htdp-beginner-reader.ss" "lang")((modname 7.7.5) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ()))) ; Exercise 7.7.5 ; area-of-ring : number (inner-radius) number (outer-radius) -> number ; assumes inner-radius <= outer-radius (check-expect (area-of-ring 0 0) 0) (check-expect (area-of-ring 2 2) 0) (check-within (area-of-ring 0 1) 3.14 .01) (check-within (area-of-ring 0 2) 12.56 .01) (check-within (area-of-ring 1 2) 9.42 .01) ; 4*3.14 for the outer circle, minus 3.14 for the inner circle (check-within (area-of-ring 2 5) 65.94 .01) ; 25*3.14 for the outer circle, minus 4*3.14 for the inner circle (define (area-of-ring inner-radius outer-radius) ; inner-radius number ; outer-radius number (- (* 3.14 outer-radius outer-radius) (* 3.14 inner-radius inner-radius)) ) ; Or, if you've already done problem 7.7.4, ;(define (area-of-ring inner-radius outer-radius) ; ; inner-radius number ; ; outer-radius number ; (- (area-of-circle outer-radius) ; (area-of-circle inner-radius)) ; )