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如图 ,∠ＢＡＣ的两边ＡＢ和ＡＣ分别与平面α相交于点Ｂ、Ｃ ,若ＡＯ⊥α于点Ｏ ,则∠ＢＯＣ叫做∠ＢＡＣ图 (1 )在平面α内的射影角。显然若∠ＢＡＣ所在的平面与α平行或垂直 ,则∠ＢＯＣ =∠ＢＡＣ或∠ＢＯＣ =1 80°。下面将探讨一个角与它的射影角的大小关系。一个角∠Ｂ
As shown in the figure, the two sides AB and AC of the BAC intersect with the plane α at points B and C, respectively. If AO⊥α is at the point O, the BOC is called the projection angle of the BAC map (1) in the plane α. Obviously, if the plane where the BAC is located is parallel or perpendicular to α, then BOC = BAC or BOC = 180°. The following will discuss the relationship between the angle of an angle and its projection angle. One Corner B