1, the number of even roots is not less than zero.

2. The three concepts of correspondence, mapping and function are * * * and different. Mapping is a special correspondence, and function is a special mapping.

3. If the expression of compound function f[g(x)] is given, the expression of function f(x) can be obtained by method of substitution. At this time, we must find the range of g(x), which is equivalent to finding the definition range of the function.

4. Inverse function method: By using the relationship between the definition domain and the value domain of the function f(x) and its inverse function f- 1(x), the value domain of the original function can be obtained by solving the definition domain of the inverse function, and the function value domain with the shape of (a≠0) can be obtained by this method.

5. The definition of parity function is the main basis for judging the parity of function. In order to judge the parity of a function, it is sometimes necessary to simplify the equivalent form of the function or application definition.