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Topic: cubic equation solver
Replies: 1   Last Post: Mar 28, 2013 5:12 PM

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Peter Pein

Posts: 1,147
Registered: 5/4/05
Re: cubic equation solver
Posted: Mar 28, 2013 5:12 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

Am 28.03.2013 09:05, schrieb Elim Qiu:
> x^3 + (=E2=88=9A6 + 2=E2=88=9A3 + 2=E2=88=9A2 -9)x + 2=E2=88=9A3 -=E2=88=9A2 -2 = 0
> has exact roots =E2=88=9A2-2, =E2=88=9A3-=E2=88=9A2, 2-=E2=88=9A3
>
> But Mathematica says:
>
> Solve[x^3 + (Sqrt[6] + 2 Sqrt[3] + 2 Sqrt[2] - 9) x + 2 Sqrt[3] -
> Sqrt[2] - 2 == 0, x]
>
> {{x -> (1/
> 2 (18 + 9 Sqrt[2] - 18 Sqrt[3] +
> I Sqrt[3 (4662 - 1252 Sqrt[2] - 1296 Sqrt[3] -

....

Hi,

as parts of your message are unreadable here, I do not know if

In[1]:= Solve[x^3 + (Sqrt[6] + 2*Sqrt[3] + 2*Sqrt[2] - 9)*x +
2*Sqrt[3] - Sqrt[2] - 2 == 0, x] // RootReduce //
ToRadicals // InputForm
Out[1]//InputForm=
{{x -> Sqrt[5 - 2*Sqrt[6]]},
{x -> 2 - Sqrt[3]},
{x -> -2 + Sqrt[2]}}

is what you expect.

Peter






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