立几中涉及动点、动直线、动平面,或结论待定的动态问题,学生常常感到十分棘手。为此,下面介绍几种常见的处理方法和技巧。 1 演绎推理法 立几贯穿用演绎推理的方法研究空间图形,因此,演绎推理自然成为处理“动态型”立几问题的常用方法。一些涉及定性或以定性为主体的问题常用此法。 例1 如图,在三棱锥S-ABC中,底面△ABC是以AC=a为底边的等腰三角形,其顶角∠ABC为变量β。∠SCA=90°,侧面 When students are involved in dynamic issues involving moving points, moving lines, moving planes, or conclusions that are to be determined, students often find it very tricky. For this reason, here are some common treatment methods and techniques. 1 Deductive reasoning approaches the use of deductive reasoning methods to study spatial patterns. Therefore, deductive reasoning has become a common method of dealing with “dynamic type” problems. Some problems involving qualitative or qualitative issues are commonly used. Example 1 As shown in the figure, in the triangular pyramid S-ABC, the bottom surface ΔABC is an isosceles triangle with AC=a as the base, and the vertex angle ∠ABC is the variable β. ∠SCA=90°, side