In practical application, it is best to indicate all the domains of variables. Because the practical application problems are likely to involve piecewise function, approximate calculation and so on, the definition domain is particularly important at this time.

Moreover, the statement definition domain can better reflect the relationship between application problems and reality. Function is inseparable from the field. If it is a positive integer or natural number, or other range, as long as it is not a real number set, high school and below should be marked.

Its main basis is:

① The denominator of the score cannot be zero.

(2) The number of even roots is not less than zero.

③ The true value of logarithmic function must be greater than zero.

④ The bases of exponential function and logarithmic function must be greater than zero and not equal to 1.