学习数学,经常碰到一个命题的条件是“充分”的,或“必要”的,或“充分与必要”的。我们知道,一个命题是由条件和结论组成的。例如:“若 a·b>0,则 a 与 b 同号”。其中,“若 a·b>0”是条件,“则与b同一号”是结论。即着月则B中,月是条方是结沦。如果我们交换条件与结论的位置,并用一羚定语气与否定 The conditions for learning math and often meeting a proposition are “adequate” or “necessary” or “adequate and necessary”. We know that a proposition consists of conditions and conclusions. For example: “If a · b> 0, a and b have the same sign.” Among them, “if a b> 0” is the condition, “and b the same number” is the conclusion. The month is B, the month is the end of the article is reduced. If we exchange the conditions and conclusions of the position, and use a calm tone and negative