Proving is a difficult thing in mathematics. Generally speaking, there is no panacea. There are even many questions that need to use some very high skills, usually not ordinary, so change a question and change a method.

So it is impossible to explain clearly how to do the proof problem here. Some proofs can only come to mind in a flash. I call this proof question "for appreciation only".

The general idea of doing proof questions is to put out all the known conditions and conclusions to be proved first, and simple questions will show the idea. Difficult problems need to find the relationship between them, and this is the most difficult part of proving problems, usually relying on various theorems, definitions, axioms, or other conclusions. This part of the content can only be trained by yourself. practice makes perfect