Chapter 1 – Reasoning in Geometry

1.2 – Points, Lines, and Planes

Essential Questions

Draw two lines that intersect in one point. Label both of the lines and the point.

Name three points that are collinear and three points that are not collinear.

Name two segments and one ray.

B D A C E

Points

A point has no size.

Points are named using capital letters.

B A C

Lines

A line is made up of an infinite number of points.

A line is named with a single lowercase letter OR by two points on the line.

l

A Line

l

or AB B

Lines

Points are collinear if they lie on the same line.

Points that are not on the same line are noncollinear.

B A D A, B, and C are collinear.

A, B, and D are noncollinear.

C E

Rays

A ray looks like a line, but has a definite starting point and extends without end in one direction.

The starting point of a ray is called the endpoint.

A ray is named using the endpoint first, then another point on the ray.

B A AB

Line Segments

A line segment is part of a line containing two endpoints and all of the points in between.

A line segment is named using its endpoints.

A AB or BA B

Planes

A plane is a flat surface that extends without end in all directions.

For any three noncollinear points, there is exactly one plane that contains all three points.

A plane is named using a single uppercase script letter or by three noncollinear points.

A C

M

Plane

M

or Plane ABC B

Planes

Points that lie in the same plane are coplanar.

Points that do not lie in the same plane are noncoplanar.

Assignment

Page 16 #9-31 odd, 32-38