平面幾何中有關“一定值”的問題,是同學感到困難的。初三、高一同學每遇到關於“一定值”的問題,班上只有極個別同學能獨立解出來,他們不知按題意分析,“一定值”是什麼,因此,摸不到問題的具體終結,無從下手解題,凡是碰到“一定值”一類的問題,總是老師講,學生聽,學生不能獨立發展這個知識,時間花了許多,費了許多力,結果不討好;我認為這原因主要在講解問題時,關於“一定值”意義,分析不夠,指示不夠,因而學生對“一定值”問題,感到摸不到頭腦。新編初中幾何93頁第13題:“等腰三角形底邊上的一點到兩腰距離之和是一定長(等於腰上的高),”書上在括弧內具體指出了問題的要求,但講解這問題時,若單純的按“等於腰上的高”囫圇吞棗的證下去,而對“一定長”為什麼是指“等於腰上的高”,不加以詳細分析、那便是為解題而解題,不能完成教學這個問題的主要目的,教學這個問題的主要目的,是為解關於“一 The problem of “a certain value” in plane geometry is that the students feel difficult. When students of grade one and grade three met questions about “a certain value”, only a few students in the class could independently solve the problem. They did not know what the “value” would be if they were analyzed according to the questions. Therefore, the specific end of the problem could not be touched. There is no way to solve the problem. Whenever you come across a question of “a certain value,” the teacher always says that students cannot listen. Students cannot independently develop this knowledge. It takes a lot of time, and it takes a lot of effort. The result is not good; I think this is mainly because When explaining the problem, the meaning of “a certain value” was not analyzed enough and the instructions were not enough. Therefore, the students felt indifferent to the question of “a certain value”. New junior high school geometry page 93, item 13: “The sum of the distance from the point on the base of the isosceles triangle to the waist is a certain length (equivalent to the height of the waist),” the book specifies the requirements of the problem in parentheses, but explains In this issue, if the simple test of “equivalent to the height of the waistline” swallows the testimony of the date, and why the “certain length” means “equal to the height of the waist,” without detailed analysis, it is to solve the problem and solve the problem. Can not complete the main purpose of teaching this problem, teaching the main purpose of this problem is to understand about "a