数学中要判断一个命题是正确的,必须经过严密的论证,而要说明一个命题是错误的,只需举出一个与结论相矛盾的例子就行了。如要否定“两个虚数之和仍为虚数”,只要举出(3+2i)+(1-2i)=4就可以了,这种与命题相矛盾的例子在数学上称为反例,下面笔者根据多年来的教学实践就反例在数学中的教学价值略谈浅见。 In mathematics, to judge a proposition is correct, it must be rigorously demonstrated, and to illustrate that a proposition is wrong, just give an example that contradicts the conclusion. If you want to deny that “the sum of two imaginary numbers is still imaginary,” just quote (3+2i)+(1-2i)=4. This example that contradicts the proposition is mathematically called counterexample, below According to the teaching practice over the years, the author discusses the teaching value of counterexamples in mathematics.