Some number, such as π and √2, can’t be written down exactly as a decimal number. When computing with such numbers, Xcas will leave them in exact, symbolic form. If you want, you can have Xcas automatically give you decimal approximations for these numbers.
You can set whether or not Xcas will give you exact or approximate values from the CAS configuration screen. Your choice will be stored in the variable approx_mode, where a value of 0 means that Xcas should give you exact answers when possible and a value of 1 means that Xcas should give you decimal approximations. Your choice will be stored in the configuration file (see subsection 3.5.10), and so can also be set there.