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上前牙铸造3/4冠牙体预备切沟要求一致的看法是:(1)唇壁的高度是舌壁的二倍,(2)唇壁的宽度是舌壁的二倍,(3)沟底位于牙本质内,(4)唇舌二壁的交角小于或等于90度。为了便于指导学生和临床操作,除以上四点要求外,再补充一点:唇壁长度为舌壁的二倍,更能直观地说明问题。利用解析几何的方法证明如下: 已知:如下图建立直角坐标系。设:A C为唇壁,BC为舌壁,C点为沟底,角ACB为唇舌二壁的交角小于或等于90度,则A、B、C三点的坐标为A(3,2),B(0,1),C(1,0)。求证:AC=2BC
(3) The height of the lip wall is twice that of the tongue wall. (2) The width of the lip wall is twice the width of the tongue wall. (3) The bottom of the ditch is located in the dentin, and (4) the angle between the two walls of the lip and tongue is less than or equal to 90 degrees. In order to facilitate the guidance of students and clinical practice, in addition to the above four requirements, to add one more point: lip wall length of the tongue wall twice, more intuitive to illustrate the problem. The method of using analytic geometry proves as follows: It is known that a Cartesian coordinate system is established as shown below. Let AC be the angle between the two walls of the tongue and the tongue less than or equal to 90 degrees, then the coordinates of A, B and C at three points are A (3,2), B (0,1), C (1,0). Prove: AC = 2BC