It is not a question of which method to use in which knowledge points, but that these four ideas should always accompany you. For example, when solving an unknown elliptic equation, we need to consider which axis is the focus, and when setting a linear equation, we need to consider whether there is a linear slope. These are all classified discussion ideas. It is impossible to deal with all the problems with a fixed idea. Only when the basic knowledge is solid, mathematical thoughts will always accompany you. I wish you progress in your grades ~ ~ ~