How to find the angle between crossed lines?

Crossed are two straight lines in three-dimensional space that do not lie in the same plane. Crossed lines do not intersect, are not parallel and do not coincide. The angle between crossed straight lines is the angle between two intersecting straight lines, which are respectively parallel to a given crossing straight. The angle between intersecting straight lines is defined through the angle between intersecting straight lines. Thus, finding the angle between intersecting straight lines is reduced to finding the angle between the corresponding intersecting straight lines in three-dimensional space.

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