Re: On the muliplication of negative numbers

The TimeLord <math-n-physics-not@xxxxxxx> wrote in message
HvCdnXUVX4kBthPVnZ2dnUVZ_sTinZ2d@xxxxxxxxxxx
Am Mon, 28 Jul 2008 13:24:20 +0200 schrieb "harry"
<harald.vanlintelButNotThis@xxxxxxx> in 1217244260_798@xxxxxxxxxxxxxxxx:

"Dirk Van de moortel" <dirkvandemoortel@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
wrote in message news:g6k7qu$r2l$1@xxxxxxxxxxxxxxxxxxxxxx
Uncle Ben <ben@xxxxxxxxxxx> wrote in message
[...]
sq.rt.(16) = 4 or -4.

No, we write
sqrt(16) = 4
and
-sqrt(16) = -4

Dirk Vdm

It's storm in a wine (or whine) glass:
http://en.wikipedia.org/wiki/Square_root Harald

I'm somewhat with Dirk Vdm here.

And so is the wiki article :-)

By tradition in math, sqrt(x) is a
function and defined as per that web site, which is consistent with Dirk
Vdm's point. However, by the same tradition, y=x^(1/2) when defined as an
inverse of x=y^2, is not really considered a function and so the solution
set of y=x^(1/2) would be y in {-x,x}.

Or formally one can define
x^(1/2) = { -sqrt(x), sqrt(x) }
and turn it into a proper function from the reals onto the powerset
of the reals. No problem.


Yeah it is usually understood by mathematicians, physicists and engineers
and quibbling is usually straining at a gnat; but sometimes we need to be
reminded of the mathematical definition.

Something on this group (I think it was called "Androcles") started
the quibbling - ant it never stopped :-)

Dirk Vdm


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