When factoring polynomials, Xcas won’t introduce complex numbers if they aren’t already being used. For example,
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but if an expression already involves complex numbers then Xcas will use them;
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Xcas also has ways of finding complex roots even when complex numbers are not present; for example, the command cfactor will factor over the complex numbers
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If you want Xcas to use complex numbers by default, you can turn on complex mode. In complex mode,
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You can turn on complex mode from the CAS configuration screen. This mode is determined by the value of complex_mode; if this is 1 then complex mode is on, if this variable is 0 then complex mode is off. This option will be stored in the configuration file (see subsection 3.5.10), and so can also be set there.