# Space

### The Summary

## A plane is determined by

- 3 non-collinear points
- A line and a point outside the plane
- 2 intersecting lines
- 2 parallel lines

## How to prove a line perpendicular to a plane ?

If a straight line is perpendicular to 2 intersecting lines in a plane then its perpendicular to the plane itself.

When Is a Line Perpendicular to a Plane? : Trigonometry & Other Math

## Relative position of a plane and a line :

- Intersecting
- Parallel
- The line is in the plane

## Relative position of 2 lines :

- Skew
- Parallel
- Intersecting
- Confounded

## How to prove that 2 planes are perpendicular ?

## Relative position of 2 planes :

- Intersecting
- Parallel
- Confounded

## Angle between 2 planes - Dihedral angle

## The Steps :

1- Find the common line.

2- Select 2 lines perpendicular from each plane to the common line.

3- Find the angle.

## Mediator Plane

## How to prove a mediator plane to a line ?

Prove that it has 3 points equidistant from the extremities of the line.

## How to prove 3 collinear points?

Prove that they belong to a line that is the intersection of 2 planes