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I am using Mathematica to find the eigenvalues of this matrix m

m = {{2, I, 1, 2}, {-I, 2, I, 1}, {1, -I, 2, 1}, {2, 1, 1, 2}}
Eigenvalues[m]

However, this gives three of the eigenvalues with a strange square root symbol whose meaning I don't understand, and when I hover over it I get even more confused

enter image description here

I have spent a while trying to figure out what this means, but I just haven't found anything on any forums or in the documentation.

m_goldberg
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Sebastian Chejniak
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    Search the docs for "root" and "root object". Apply N to get a numeric value. – ciao Oct 01 '20 at 18:37
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    The tooltips show that they are expressions with the head Root. The documentation can take it from there. – Bob Hanlon Oct 01 '20 at 18:45
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    Perhaps helpful: https://mathematica.stackexchange.com/questions/13767/how-do-i-work-with-root-objects – Michael E2 Oct 01 '20 at 18:46
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    You can turn off the cute typesetting with Unprotect@BoxForm`UseApproximations; BoxForm`UseApproximations = False; Protect@BoxForm`UseApproximations; – Michael E2 Oct 01 '20 at 18:48
  • an accurate number. Therefore, MMA gives an expression, whose root is the answer. You may request an approximative answer in form of a machine number by the operator "N". – Daniel Huber Oct 01 '20 at 18:55

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