一、从对应元素入手例1如图1,在△ABC中,若AB⊥AC,AD⊥BC,则AB~2=BD·BC.类比该命题,如图2,在三棱锥A′-B′C′D′中,A′D′⊥平面A′B′C′,若点A′在△B′C′D′所在平面内的射影为M,则可推理出什么结论?推理由题意可知,△ABC与三棱锥A′-B′C′D′的对应元素有: First, from the corresponding element to start a case as shown in Figure 1, △ ABC, if AB ⊥ AC, AD ⊥ BC, then AB ~ 2 = BD · BC analogy to the proposition, as shown in Figure 2, ’C’D’, A’D’⊥ plane A’B’C ’, if the point A’ △ B’C’D ’in the plane of the projection is M, what conclusion can be deduced? Reasoning questions It can be seen, △ ABC and triangular pyramid A’-B’C’D ’the corresponding elements are: