投影角与两直线空间夹角关系的判定定理

JUDGMENT THEOREM OF RALATION OF PROJECTIVE ANGLE AND TWO LINES' SPACE ANGLE

空间两直线所成的角度，投影时并非不变量，其投影角可大于、小于或等于其空间夹角．本文通过空间分析和解析计算推证出构成空间角度的两直线当中有一条直线与投影面平行时，其投影角的判定定理组．

The angle which formed of two lines in space is a constant in projetiveangle may be great,little or equal its space angle. The judgment theorem of projetive angle isinferred through space analysis and calculation when one line in both which formed space an-gle is parallel with projective surface in this article.