Geometry Notes
1.3 Points, Lines and Planes
Mr. Belanger
Point
Point – dot with no measurable size
(doesn’t affect area or length)
Space
Space – set of all points in 3-D
(think air particles)
Line
Line – straight connection of two points that
goes forever in opposite directions
(should have arrows on both ends)
Collinear
Collinear – points that lie on the same line
Points COD are collinear.
Points AOB are collinear.
Name three that are not collinear.
COB, DAB
( O is point at intersection)
Plane
Plane – flat 2-D space that goes on forever.
(think wall or white board)
Coplanar – two or
more points on the
same plane.
Undefined Terms
Point, line, plane are all undefined terms. Meaning they are
defined by real words, but their concepts cannot be taken
literally and are just accepted as fact.
Like a point has no size, even though you can see it
A line and a plane have no thickness, even though you can see it
Postulate (axiom)
is an accepted statement of fact
1-1: through any two points there is only one line
1-2: if two lines intersect, they cross at one point
1-3: if two planes intersect they form a line
1-4: through any three non-collinear points there is
only one plane