Hi all and happy new year

First I am a beginner in Maple and I want to solve an equation, but I obtain a complexe result with this _Z, my equation is 6th order and the unkown is alpha:

I tried these instructions but without resul:

z := solve(my eq,alpha)
zsol := allvalues(z)
evalf(zsol)

And I get this result

I want a simple result and what is the meaning of _Z