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Re: FindInstance puzzler


On 27 Nov 2007, at 17:05, Andrzej Kozlowski wrote:

> Reduce[2*y*I*Sqrt[x] + 2*(y - I*Sqrt[x]) == 0, {x, y}, Reals]

This should have been:


In[17]:= Reduce[2*y*I*Sqrt[x] + 2*(y - y*I*Sqrt[x]) == 0,
   {x, y}, Reals]
During evaluation of In[17]:= Reduce::nddc:The system 2 \[ImaginaryI]  
Sqrt[x] y+2 (y-\[ImaginaryI] Sqrt[x] y)\[LongEqual]0 contains a  
nonreal constant 2 \[ImaginaryI]. With the domain \ 
[DoubleStruckCapitalR] specified, all constants should be real. >>
Out[17]= Reduce[2*I*Sqrt[x]*y + 2*(y - I*Sqrt[x]*y) == 0,
   {x, y}, Reals]


but it other than that it does not change anything. Note that:

Reduce[Simplify[2*y*I*Sqrt[x] + 2*(y - y*I*Sqrt[x]) == 0], {x, y},  
Reals]
y==0

What I really mean tto say is: wouldn't it be a litte better to first  
automatically apply Simplify in such situation to see if the I's could  
be got rid of?

Andrzej Kozlowski




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