Section 1-2 Points, Lines and Planes

A Point A point represents a position in space. It is named using capital printed letters. A

A Line Two points determine a line. A line is an infinite set of points that extends in two directions without ending. It is named using a single lower case cursive letter or by two points on the line, AB l AB

Noncollinear Points that ARE NOT on the same line. Collinear Points that are on the same line.

A Plane At least three noncollinear points determine a plane. A plane is an infinite amount of points that creates a flat surface that extends without ending. Has no thickness Usually pictured as a parallelogram, although it has NO edges It is named using a capital cursive letter M A B C

Noncoplanar Points in the same plane Coplanar Points NOT in the same plane

Example 1 D F A B C G a.Name collinear points b.Name coplanar points c.Name 3 points that are not coplanar A, B, C A, B, D, F, C C, G, F

Line Segment Part of a line consisting of two endpoints and all points in between It is named using the two endpoints, AB AB

Ray Part of a line with an initial point and all points going in one direction It is named using the endpoint first followed by another letter on the ray, AB Why can’t we name the ray above as BA? AB

Opposite Rays Have the same initial point going in opposite directions (180°) CA and CB ACB

Intersection Two or more geometric figures intersect if they have one or more points in common. Line l and k intersect at point p lk p