Question: Float(undefined) error when trying to find Real part

Hi, was wondering if any of you could help me, when I try and find the real part of a function to plot, I get a float(undefined) error, however by just using evalf if gives gives me the real and comlex parts.

zetaroots.mw

The function i want to find realy parts for is f(x).

 

Thanks,

Matt

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