导言 :前面我们学习了四种命题之间的关系 ,我们知道 ,将一个命题“若 ｐ则 ｑ”的条件和结论交换 ,并同时否定所得到的新命题“若┒ ｑ则┒ ｐ”就是原命题的逆否命题 ,根据这一法则 ,请同学们写出命题 :“若ａ ,ｂ全为 0 ,则ａｂ =0”的逆否命题 .抽一名中等水平的学生甲在黑 Introduction: In front of us, we learned the relationship between four propositions. We know that if we exchange the conditions and conclusions of a proposition “If p then q,” and at the same time negate the new proposition, “If ┒ q ┒ ┒ p” is the original The inverse proposition of the proposition, according to this rule, ask the students to write a proposition: “If a, b all 0, then ab =0” negative no proposition. Draw a middle level student A in black