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问题 已知ＰＡ⊥平面ＡＢＣ,如图1,我们称△ＡＢＣ是△ＰＢＣ在平面ＡＢＣ上的射影三角形,那么这两个三角形的顶角∠ＢＡＣ与∠ＢＰＣ哪一个大呢? 这个问题看起来非常简单,凭直觉都认为∠ＢＡＣ∠ＢＰＣ.事实并非如此,剖析如下.图2∠ＢＡＣ∠ＢＰＣ的情形1)过Ａ作ＡＤ⊥
The problem is known as the PA plane ABC, as shown in Figure 1. We call △ABC the projective triangle of △PBC in the plane ABC. Which of the two triangle’s top angles ∠ BAC and ∠BPC is larger? This problem looks very much Simple, intuition all think that ∠ ∠ ∠ ∠ ∠ PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC PC ∠ ∠ ∠ ∠ ∠ ∠