解题过程实际上是一个不断转化的过程,在转化过程中,通常要求等价转化,这样可使得到的解不至于扩大或缩小.然而,有时候寻求原问题的等价条件很难或很繁,不便于求解,此时若能利用原问题的一个较弱的必要条件求解,再作充分性验证,则能化难为易,化繁为简,提高解题效率.一、利用必要条件求参数值或求参数的范围 Problem solving process is actually a continuous process of transformation, which usually requires equivalent transformation, so that the solution can not be expanded or contracted. However, sometimes it is difficult or very difficult to find the equivalent conditions of the original problem If it can be solved by a weak necessary condition of the original problem and then fully verified, it will be easier to make things easier and more complex to improve the efficiency of solving problems. Range of parameters or parameters