[racket] HTDP 2nd edition exercise 4.2.3 - floating point issues

;; equation3 : number  ->  boolean
;; to determine whether n is a solution for 2n^2  =  102
(define (equation3 n)
  (=~ (* 2 n n) 102 .001))


-- Matthias



On Oct 22, 2013, at 8:40 AM, Bo Gus <forumangus at gmail.com> wrote:

> equation 2 is 2n^2 = 102 so I implement like this:
> 
> ;; equation3 : number  ->  boolean
> ;; to determine whether n is a solution for 2n^2  =  102
> (define (equation3 n)
>   (= (* 2 n n) 102))
> 
> And my answer is the same as per the online answer.  so great.
> 
> But how can I check a valid answer.
> 
> Eg if I do:
> 
> (equation3 (sqrt 51))
> >false
> 
> same using - square root 51.  
> 
> How can I fix this?  Is the only way to do a range check?  Eg have some sort of tolerance - eg between 0.01 above and below answer?  Any other ideas?
> 
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