parallel and perpendicular planes
Theorem 1. If a plane (π) intersects two parallel planes (ϱ, σ), the intersection lines are parallel
.
Proof. The intersection lines cannot have common points, because ϱ and σ have no such ones. Since the lines are in a same plane π, they are parallel.
Theorem 2. If a plane (π) contains the normal (http://planetmath.org/PlaneNormal) (n) of another plane (ϱ), the planes are perpendicular (http://planetmath.org/DihedralAngle) to each other.
Proof. Draw in the plane ϱ the line l cutting the intersection line perpendicularly and cutting also n. Then l must be perpendicular to n and thus to the whole plane π (see the Theorem in the entry normal of plane). Consequently, the right angle formed by the lines n and l is the normal section of the dihedral angle formed by the planes π and ϱ. Therefore, π⊥ϱ.
Title | parallel and perpendicular planes |
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Canonical name | ParallelAndPerpendicularPlanes |
Date of creation | 2013-04-19 15:18:51 |
Last modified on | 2013-04-19 15:18:51 |
Owner | pahio (2872) |
Last modified by | pahio (2872) |
Numerical id | 10 |
Author | pahio (2872) |
Entry type | Theorem |
Classification | msc 51M04 |
Related topic | PlaneNormal |
Related topic | NormalOfPlane |
Related topic | ParallelismOfTwoPlanes |