给定的两个命题A和B:若A真时B真,则称A是B的充分条件,B是A的必要条件.若A真时B真,且B真时A真,则称A是B的充要条件.“充要条件”是高中数学中的重要知识点,它灵活性强,对学生的逻辑思维能力和判断 Given two propositions A and B: if A is true B is true, then A is a sufficient condition for B and B is a necessary condition for A. If A is true B is true and B is true A is true, then A Is a necessary and sufficient condition of B. “Sufficient and necessary conditions ” is an important knowledge point in high school mathematics, it is flexible, and students’ logical thinking ability and judgment