论文部分内容阅读
旋转变换是几何证题中一种很重要的解题技巧.在同一平面内,将图形的某一部分按特定的条件旋转一个角度,把分散的条件和结论相对集中,使图形中的相关部分发生新的联系,使已知和未知得到更好的沟通,从而使问题化难为易,化繁为简,迎刃而解.例1如图1,在△ABC中,AB=AC,D是△ABC内一点,∠ADB>∠ADC,求证:DC>BD.分析:条件中有共点且相等的边AB和AC,可将△ABD以点A为中心、逆时针旋转∠BAC的度数到△ACE的位置,从而只要证DC>CE即可.
Rotational transformation is a very important problem in the geometry of the problem solving skills in the same plane, a certain part of the graphics by a specific rotation angle, the conditions and conclusions of the relative dispersion, so that the relevant parts of the graph occurs New contacts make known and unknown get better communication, so that the problem is difficult, easy to solve, easy to solve.Example 1 As shown in Figure 1, △ ABC, AB = AC, D is △ ABC within a point , ∠ADB> ∠ADC, verify: DC> BD. Analysis: There are a total of points and equal edges AB and AC in the condition, △ ABD can be centered around point A and counterclockwise to rotate 度BAC to △ ACE , So as long as the card DC> CE can.