;; 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 15.3.3) (read-case-sensitive #t) (teachpacks ((lib "testing.ss" "teachpack" "htdp"))) (htdp-settings #8(#t constructor repeating-decimal #f #t none #f ((lib "testing.ss" "teachpack" "htdp")))))
; Worked exercise 15.3.3
; distance-to-0 : posn -> number
(define (distance-to-0 the-point)
  ; the-point                  a posn
  ; (posn-x the-point)         a number(x)
  ; (posn-y the-point)         a number(y)
  ; (sqr (posn-x the-point))   a number (x^2)
  ; or we could have written
  ; (* (posn-x the-point) (posn-x the-point))
  ; (sqr (posn-y the-point))   a number (y^2)
  ; (+ (sqr (posn-x the-point)) (sqr (posn-y the-point)))
  (sqrt (+ (sqr (posn-x the-point))
           (sqr (posn-y the-point))))
  )
(check-within (distance-to-0 (make-posn 0 0)) 0 .01)
(check-within (distance-to-0 (make-posn 6 0)) 6 .01)
(check-within (distance-to-0 (make-posn 0 4.3)) 4.3 .01)
(check-within (distance-to-0 (make-posn 3 4)) 5 .01)
(check-within (distance-to-0 (make-posn 4 7)) (sqrt 65) .01)


(generate-report)