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

 From: Matthias Felleisen (matthias at ccs.neu.edu) Date: Tue Oct 22 08:53:28 EDT 2013 Previous message: [racket] HTDP 2nd edition exercise 4.2.3 - floating point issues Next message: [racket] HTDP 2nd edition exercise 4.2.3 - floating point issues Messages sorted by: [date] [thread] [subject] [author]

```;; 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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```

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