“要什么,找什么”是一种讲究实效的思考方法。在“要什么,找什么”的时候必须注意靠拢已知条件,或及时运用已知条件。用在数学证题中,最简单的思索线路是:“要B,就要找C;要C,就要找D;要D,去逐步找到已知条件A。”从而完成A→B的证明。这里所找的是要证结论的各种可能的充分条件(包括充要条件) “What to look for, what to look for” is a kind of practical method of thinking. When “what to find, what to look for” must pay attention to move closer to known conditions, or apply known conditions in a timely manner. The simplest way to think about mathematical proofs is: “If you want B, you need to find C; if you want C, you need to find D; if you want D, go step-by-step to find the known condition A.” Thus completing the A → B proof . What we are looking for here are all possible sufficient conditions (including necessary and sufficient conditions) to prove the conclusion.