Points, lines, planes
Identify and describe points, lines, and planes and how they relate.
Objective
Identify and describe points, lines, and planes and how they relate.
What it means
A point is a location with no size. A line is a straight, one-dimensional path extending infinitely in two directions. A plane is a flat, two-dimensional surface extending infinitely in all directions.
Key terms
- Point
- A location with no size, named by a capital letter.
- Line
- A straight path of points extending infinitely both ways.
- Plane
- A flat surface extending infinitely, named by three non-collinear points.
- Collinear
- Points that lie on the same line.
- Coplanar
- Points or lines that lie in the same plane.
Rules to remember
- Two points determine exactly one line.
- Three non-collinear points determine exactly one plane.
- A line contains infinitely many points.
Step by step
- 1Identify the objectsDecide whether you are looking at a point, line, segment, ray, or plane.
- 2Check collinearitySee if the points lie on one straight line.
- 3Check coplanaritySee if the objects share a common flat surface.
Common mistakes
- Confusing collinear (same line) with coplanar (same plane).
- Thinking any three points determine a plane — they must be non-collinear.
Tips
- Picture a line as a laser beam with no endpoints, and a plane as an infinite flat sheet of paper.