At 05:19 AM 2/14/00 +0100, Berthold Heinrich wrote:
>Can you help me?
>
>1. if you approximate pi, you get the wrong number
>
>3.14159292035
>
>
>2. If you try to solve the square-root-equation
> 10
>‹(5·x - 56) = ‹(x + 12) - ———————————
> ‹(x + 12)
>
>x : Real (0, –)
>
>you get the wrong solution x=-13
>
>[x = 13, x = -13]
>
>Can you help me?
>
>Berthold Heinrich
>
The first question has already been answered by David. The only thing I
want to supplement is that the assignment
PrecisionDigits := 12
alone will suffice, because the variable NotationDigits gets the same value
automatically.
As for your second question I would like to point out that (like it or lump
it!) declaring the domain of variables will not affect subsequent SOLVE
commands involving those variables (at least not in the way you thought!)
The declaration of a variable serves a different purpose. For example,
DERIVE will only simplify the expression sin(n pi) to 0, if you declared n
as an integer before (which makes sense, doesn't it?)
On the other hand, it's easy to get a vector of all positive solutions of
your equation by simplifying
select(x>0,x,rhs(solve(sqrt(5x-56)=sqrt(x+12)-10/sqrt(x+12),x)))
There may be other cases though, where things are not that simple.
Cheers, Johann
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