Question

why is it appropriat to use when culculating a temperature range that is as much above and below room temperature ?

Answer 1

While calculating any other value we should use the temperature range that is above as well as below the room temperature so that we can see the behaviour of the quantity in all temperature ranges and can analyse its average value at the room temperature only. Also some of the quantities behaves differently at higher temperature and lower temperature from that is expected, i.e. some of the quantities don't follow the linear behaviour with temperature(for example thermal expansion is applicable only for small temperature and not for higher temperature), thus to know all the properties of such kind of the unknown objects its better to use wide range of temperatures which include both very high as well as very low temperature