x = -2, 3 and 5 are the real roots.
There are also complex roots x = 3 + i and 3 - i.
I'm lazy. I used
http://xrjunque.nom.es/precis/rootfinder.aspx
All all zeros for the following function f(x)= x5- 10x4 + 23x3 +56x2 -290x + 300
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