平面图形在依一定规律运动,变化时,有些量不发生变化,研究这些不变量的问题称为定值问题.讨论定值问题,能更深刻地理解图形性质.提高学习兴趣,发展思维能力.解决此类问题,有以下几种方法:(1)当定值已知时,只需结合其特征,结合题中给出的条件,经过适当的计算,便可使问题得证(如下例1).()当定值未知时,可把题目中的变动元 Plane graphics in accordance with a certain regular exercise, changes, some of the amount does not change, the study of these invariants called the fixed value problem. Discuss the valuation problem, a deeper understanding of the graphic nature. To solve such problems, there are several ways: (1) When the valuation is known, just combine the characteristics, combined with the conditions given in the title, through proper calculation, can make the problem proved (as in Example 1 ) (.) When the valuation is unknown, the subject of change yuan