http://www.ck12.org Chapter 1. Basics of Geometry
a) PlaneBDG, PlaneKAG, among several others. Any combination of three coplanar points that are not collinear
would be correct.
b)
←→
ABor any combination of two of the lettersA,CorBin any order.c) Yes, they lie on the same line.Yes, you need three points to create a plane, so any two or three points are coplanar.
d) Yes, any three points are coplanar.
e)A,C,DandEwould be non-collinear. Since three points define a plane, any three of the points would line in the
same plane but the fourth must not.
Endpoint:A point at the end of a line.
Line Segment:Part of a line with two endpoints. Or a line that stops at both ends.
Line segments are labeled by their endpoints,ABorBA. Notice that the bar over the endpoints has NO arrows. Order
does not matter.
Ray:Part of a line with one endpoint and extends forever in the other direction.
A ray is labeled by its endpoint and one other point on the line.
Of lines, line segments and rays, rays are the only one where order matters. When labeling, always write the endpoint
under the side WITHOUT the arrow,
−→
CDor←−
DC.
Intersection:A point or set of points where lines, planes, segments or rays cross each other.
Example 5:How do the figures below intersect?
Solution:The first three figures intersect at a point,P,QandR, respectively. The fourth figure, two planes, intersect
in a line,l. And the last figure, three planes, intersect at one point,S.
Example 6:Answer the following questions about the picture to the right.