1: direct method: from the range of independent variables, the range of values is derived, that is, directly. This doesn't need an example, does it?

2. Separation constant method

3. Matching method (or maximum method)

Find the maximum and minimum values,

4. Discriminant method, using the idea of equation, has real root evaluation domain according to quadratic equation.

5 alternative methods

6. Image method, drawing directly to see the range.

7-domain method for finding inverse function