-。 -Landlord, I am very entangled in this question. In fact, when you solve math problems, you should pay attention to each problem by writing a word proof and a "proof" equation to solve it, that is, letters belong to one side and numbers belong to the other. ~ this will do. Now you are not very strict about the format of the second grade, so pay attention. In fact, the format of a topic can bring you ideas to solve the problem. . . . . That's all. I hope to adopt it.