Different answers from 'roots' & 'solve' command?

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Subham Shit
Subham Shit 2015-4-7
编辑： Matt J 2015-4-7
>> R=roots([3 0 0 0 0 4 1])
R =
0.9017 + 0.6256i
0.9017 - 0.6256i
-0.2767 + 1.0147i
-0.2767 - 1.0147i
-1.0000 + 0.0000i
-0.2502 + 0.0000i
>> R(R == real(R))
ans =
-1.0000
-0.2502
>> solx = solve(3*x^6 + 4*x + 1==0, x)
solx =
-1
RootOf(z^5 - z^4 + z^3 - z^2 + z + 1/3, z)[1]
RootOf(z^5 - z^4 + z^3 - z^2 + z + 1/3, z)[2]
RootOf(z^5 - z^4 + z^3 - z^2 + z + 1/3, z)[3]
RootOf(z^5 - z^4 + z^3 - z^2 + z + 1/3, z)[4]
RootOf(z^5 - z^4 + z^3 - z^2 + z + 1/3, z)[5]
>> solx(solx == real(solx))
ans =
-1
>>
  1 个评论
Subham Shit
Subham Shit 2015-4-7
编辑：Subham Shit 2015-4-7
Using 'roots' I am getting 2 real solution but using 'solve' I am getting 1 real solution of same equation. How is that possible?

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采纳的回答

Matt J
Matt J 2015-4-7
编辑：Matt J 2015-4-7
SOLVE was not able to find a closed symbolic form for all the roots (because one doesn't exist for this polynomial). It therefore cannot assess whether the ones not in closed form are real.

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