Re: A little lesson for sqrt(144) year olds.
From: Dirk Van de moortel (dirkvandemoortel_at_ThankS-NO-SperM.hotmail.com)
Date: 07/06/04
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Date: Tue, 06 Jul 2004 08:58:48 GMT
"Randy Poe" <poespam-trap@yahoo.com> wrote in message news:df76407e.0407052137.5f8d2992@posting.google.com...
> "Androcles" <androc1es@nospamblueyonder.co.uk> wrote in message news:<x5jGc.331$rk4.5112897@news-text.cableinet.net>...
> > "The Ghost In The Machine" <ewill@aurigae.athghost7038suus.net> wrote in
> > message news:rmjor1-8ip.ln1@lexi2.athghost7038suus.net...
>
> > | Carefully taking square roots, one gets:
> > |
> > | x + b/(2a) = +/- sqrt(b^2 - 4ac) / (2a)
> > |
> > | and the formula follows.
> >
> > Goodness me! I'm told sqrt is always positive by Dinky the Deranged.
> > Where did the minus sign in front of it come from?
>
> The minus sign is the thing you put in front of a positive
> value to get a negative value.
>
> Thus, x+ b/(2a) can be either sqrt(b^2 - 4ac) / (2a) or its
> additive inverse, -sqrt(b^2 - 4ac) / (2a). In both cases,
> the sqrt represents a negative quantity.
[typo: negative ==> positive]
He will love it - if he notices ;-)
> That's why putting
> a minus sign in front of it represents a negative quantity.
>
> Quiz for you: Is 3 positive or negative?
> Is -3 positive or negative?
> Suppose I tell you x is positive. What sign is -x?
> Suppose I tell you sqrt(x) is positive. What sign is -sqrt(x)?
>
> If I tell you -3 is negative, does that make 3 negative?
> If I tell you -sqrt(3) is negative, does that make sqrt(3) negative?
>
> Take all the time you need.
Even that will not be sufficient.
Duck and cover.
Dirk Vdm
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