Zhang Yu has the titles of "Yu Ge" and "Shen Yu" among the students who take the postgraduate entrance examination, and has a humorous personality. "Give up the postgraduate entrance examination immediately" is a sentence he often involves when talking about some difficult problems in his lectures. Many students are already a little annoyed when they hear the problem. Brother Yu's sentence is both funny and can rekindle students' interest. Or sometimes students can't do some simple questions, and Brother Yu will throw out this famous saying, because a person can't do such simple questions and can give up the postgraduate entrance examination. Zhang Yu, a graduate math teacher, has many years of experience in advanced mathematics teaching and postgraduate counseling, and has published many papers in national core journals.