The problem of the conclusion is true only if it in any particular case is true, this is the replacement value theory, especially value method is essentially a form of deductive reasoning thinking, has the function of ideas. How to select special cost? Depending on the specific issues, there is no fixed rule, its flexibility is stronger, often from the topic, dry, or choices, by considering the special situation"specialization", the question even structure accord with inequality problem of special function, special, special series, special graphics, special geometry, etc.%众所周知，问题的一般性结论为真的前提是它的任一特殊情况下为真，这是特值替换(或赋值法)的理论依据，特值法本质上是一种演绎推理思维形式，具有函数的思想观点。特殊值如何选取？视具体问题而定，没有一成不变的规律，它的灵活性较强，常从题干或选择支出发，通过考虑特殊情形把问题“特殊化”，甚至构造符合题设的特殊函数、特殊不等式、特殊数列、特殊图形、特殊几何体等。
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