Some numbers, such as π and √2, can’t be written down exactly as decimal numbers. When computing with such numbers, by default Xcas leaves 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 gives you exact or approximate values by using the CAS configuration screen (see Section 3.5.7). Your choice will be stored in the variable approx_mode, where a value of 0 means that Xcas will give you exact answers when possible and a value of 1 means that Xcas will give you decimal approximations. Your choice will be stored in the configuration file (see section 3.5.10), and so can also be set there.