As long as this straight line is in one of the planes and the plane is parallel, it can be directly concluded that the line is parallel. When faces are parallel, in fact, any straight line on one face is parallel to the other face.

If two planes have no common points, they are said to be parallel. Two planes are parallel if their perpendicular lines are parallel. If two intersecting straight lines in one plane are parallel to another plane, then the two planes are also parallel.

The perpendicular lines of two parallel planes are parallel or coincident. It is proved that the case of coincidence is easy to prove, and the case of parallelism can be judged that a straight line is perpendicular to both planes according to Theorem 3, and then two straight lines are parallel according to the vertical nature of lines and planes.

Extended data:

Theorem of plane parallel correlation;

1 If two planes are perpendicular to the same straight line, then the two planes are parallel.

2. If two intersecting straight lines in a plane are parallel to another plane, then the two planes are parallel.

3. If two intersecting straight lines in one plane are parallel to two intersecting straight lines in another plane, then the two planes are parallel.

4. Two planes are parallel, and any straight line in one plane is parallel to the other plane.

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