数学证明中常常采用直接证法,由已知到结论,顺理成章。然而对于间接证法的反证法,大多数同学不能深刻理解,难以走出直接证法的局限。其实,反证法可以解决直接证法难以解决的问题。正面强攻不成,迂回包抄获胜。反证法的基本思想是:对于相互矛盾的两个判断,如果其中一个错了,那么另一个一定是对的,这是逻辑学上的排中律,不能同假,必有一真。据此,要证明一个数学命题的成立,只要证明其反面 In mathematics proofs, direct evidence is often used. From the known to the conclusion, it is a matter of course. However, for the counter-evidence method of indirect evidence, most students cannot understand it profoundly and it is difficult to get out of the limitations of direct evidence. In fact, the counter-evidence method can solve the problems that are difficult to solve with direct evidence. Positive storms failed, and they made a win. The basic idea of ​​counter-evidence is that if one of the two contradictory judgments is wrong, then the other must be correct. This is the logical law of expulsion, which cannot be the same as false. There must be a truth. According to this, to prove the establishment of a mathematical proposition, just to prove its negative side