Preliminary Concepts

Planes are "flat" They extend in all directions.

Definition- The point of intersection of a line and a plane is called the foot of the line.

Four Ways to Determine a Plane

Postulate-Three noncollinear points determine a plane.

Theorem- A line and a point not on the line determine a plane.

Theorem- Two intersecting lines determine a plane.

Theorem- Two parallel lines determine a plane.

Two Postulates Concerning Lines and Planes

Postulate- If a line intersects a plane not containing it, then the intersection is exactly one point.

Postulate- If two planes intersect, their intersection is exactly one line.