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

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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