1. matching method: convert it into a quadratic function and evaluate it by using the characteristics of the quadratic function; Often converted into:;

2. Inverse solution (inverse solution): through the inverse solution, the value range is expressed and reused, and the value range is obtained by solving the inequality; Commonly used to solve, such as:

3. Substitution method: transform it into a function that can be evaluated by variable substitution, and simplify it into an idea;

4. Triangular Bounded Method: Transform it into a function containing only sine and cosine, and use the boundedness of trigonometric function to find the domain;

5. Basic inequality method: transforming into a shape, such as: using the mean inequality formula to find the domain;

Monotonicity method: the function is monotonous, and the domain can be evaluated according to the monotonicity of the function.