Range and maximum value of function: the range of function is taken from the definition range and corresponding rules. No matter what method is adopted to find the range of function value, the definition range should be considered first. Common methods for finding function value fields are as follows:

(1) direct method: also known as observation method, for western numbers with simple structure, the range of functions can be directly observed by applying the properties of inequalities to the analytical expressions of western numbers.

(2) substitution method: the given complex western number is transformed into another simple function re-evaluation domain by algebraic or triangular substitution. If the resolution function contains a radical, algebraic substitution is used when the radical is linear and trigonometric substitution is used when the radical is quadratic.