平面几何中的定值问题一般是指这样一种类型的问题:在所研究的图形中,一部分元素固定,而另一部分元素可以变动,其中角度、线段或两变动线段的和、差、积、比等,它的值始终保持不变。证明定值问题,常可先将研究对象置于特殊位置,通过对这个特殊情况的研究,确定出定值的大小,再证明在一般情况下我们所研究的对象的值等于确定的值。下 The problem of fixed values ​​in plane geometry generally refers to a type of problem in which some of the elements are fixed and the other elements can be varied in the studied pattern, where the sum, difference, Ratio, etc., its value remains unchanged. To prove the fixed value problem, we often place the research object in a special position. By studying this special case, we determine the fixed value, and prove that under normal circumstances, the value of the object we study is equal to the determined value. under