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Lesson 1-1
Points, Lines, and Planes
Building Blocks of Geometry
Definition: The three building blocks of geometry are
points, lines, and planes.
Points
How to sketch a dot:
How to label:
* Use capital printed letters.
AB
CA
* Never label two points with the same name (in the same sketch).
Definition: It is the most basic building block of geometry. It has no size. It has only location.
Lines
How to sketch:
How to label:
1- small “script” letter
•must have arrowsat both ends
2- any two points on the line
(Two methods)
A B C
n
AB
BA
AC
CA
BC
CB
ABC
Possible Names:
??
??
?
?
Definition: It is straight continuous arrangement of infinitely many points. It has infinite length but no thickness. It extends forever in two directions.
Planes
How to sketch:
How to label:
* horizontal* vertical
1- capital “script” letter
2- any three points on the plane
(Two methods)
* other
horizontal “edges”
vertical “edges”
M
PN
Definition: It has length and width but no thickness. It is a flat surface that extends infinitely along its length and width.
Collinear Points
Collinear points are points that lie on the same line. (The line does nothave to be visible.)
A
BC
non-collinearcollinear
A B C
Definition:
CoplanarDefinition: Points on the same plane
Example:• Points D, E, and F are coplanar.
D F
E
Line Segment
Consists of two endpoints and all points between
How to sketch:
How to name:
Definition:
AB
AB or BA
The symbol AB is read as "segment AB".
Congruent Segments
Definition: segments with equal lengths( the symbol for congruent is = )~
Numbers are equal. Objects are congruent.AB: the distance from A to B ( a number )AB: the segment AB ( an object )
AB
D
CCongruent segments can be marked with . . .
Correct notation:
Incorrect notation:
AB = CD AB CD
AB = CDAB CD
Midpoint
A point that divides a segment into two congruent segments.
Definition:
EDF
If DE EF , then E is the midpoint of DF.
Segment Bisector
Any object that divides a segment into two congruent parts which is the bisector of the segment.
Definition:
B
E
D
FA
BE
D
FA
E
D
A F
B
AB bisects DF. AB bisects DF.
AB bisects DF.
Ray
Definition:
( the symbol RA is read as “ray RA” )
How to sketch:
How to name:
R
A R A Y
RA ( not AR )
RA or RY ( not RAY )
A ray begins at a point and extends infinitely in one direction.
