Introduction to "20 13 PubMed Mathematics Formula Mystery": Mathematical formula is the foundation of mathematics, and whether you master it skillfully is directly related to the results of mathematics examination. Spending 20% of the time mastering mathematical formulas is equivalent to mastering 80% of the contents of the math exam, which is equivalent to getting 80% of the scores. In order to help students memorize these mathematical formulas skillfully, the Mystery of Mathematical Formulas for 20 13 Postgraduate Entrance Examination is classified by charts according to the requirements of the national postgraduate entrance examination outline, and the mathematical formulas that must be mastered are sorted out according to the frequency of questions in test sites over the years and the law of memory-understanding-mastery, and the classic real questions are summarized. Candidates can practice according to their own actual situation, which is believed to be helpful for the review of postgraduate entrance examination.