Decision theorem

A straight line out of the plane is parallel to a straight line in the plane, then the straight line is parallel to the plane.

Property theorem

If a straight line is parallel to a plane, then the intersection of any plane passing through this straight line and this plane is parallel to this straight line.

(2) The plane is parallel to the plane.

Decision theorem

Two intersecting straight lines in one plane are parallel to the other plane, so the two planes are parallel.

Property theorem

If two parallel planes intersect the third plane at the same time, their intersection lines are parallel.

(3) The straight line is perpendicular to the plane.

Decision theorem

A straight line is perpendicular to two intersecting straight lines on a plane, so this straight line is perpendicular to the plane.

Property theorem

Two straight lines perpendicular to the same plane are parallel.

(4) The plane is perpendicular to the plane.

Decision theorem

If one plane intersects the perpendicular of the other plane, the two planes are perpendicular.

Property theorem

If two planes are perpendicular, a straight line perpendicular to the intersection in one plane is perpendicular to the other plane.